Boston cream pie is probably one of my all time favorites. Growing up in the Boston area, it was certainly my dessert of choice, as well as my donut of choice at Dunkin’ Donuts! For me, the pastry cream filling is my everything. I just love it! Recently, I made a bunch of Boston cream pies for various family and friends get togethers. Separately, I had been thinking about upping my s’mores game. Suddenly, a light went off — I had to combine the two! Hence, the S’Mores Boston Cream Pie. Graham cracker cake sandwiching an outrageous chocolate pastry cream, all topped with a homemade marshmallow creme frosting. I had to make this dream become a reality! So, … I did!
What is Boston Cream Pie?
Let’s back things up a bit to make sure we are all on the same page. Boston cream pie is not a pie. It’s actually a cake. It’s just one of those crazy things in life that we must accept. Traditionally, it is a two-layer vanilla sponge cake with vanilla pastry cream in between the two layers. The top layer is usually a dark chocolate fondant (poured fondant) or chocolate ganache. I actually prefer the top with a fudge frosting rather than ganache, but that’s just me. Wikipedia has a brief history about its creation.
How to Make S’Mores Boston Cream Pie
Making a S’Mores Boston Cream Pie is really not that difficult. It is made from three components: the cake, the pastry cream, and the marshmallow creme. The cake is the easiest thing to make. The pastry cream and marshmallow creme are not difficult to make, but just require a bit more precision. Each component does not take long to whip up, and you can make the cake and pastry cream in advance. To make life even easier, you can assemble the cake in advance and store it in the refrigerator, making this a great dessert for a soiree.
I will address each of the three components in the order in which I recommend making them:
1. Make the Chocolate Pastry Cream
Making pastry cream is not a difficult task, and really only takes a few minutes. It’s a great arm workout too! I developed this pastry cream recipe specifically to be rich in chocolate flavor. I think it makes the dessert as a whole super decadent.
You only need a handful of ingredients to make chocolate pastry cream:
- Milk: Use whole milk for the best flavor and consistency in pastry cream.
- Sugar: You will need to divide the total amount of sugar, but you can just eyeball it.
- Cocoa: I highly recommend Dutch process cocoa for its deep, rich chocolate flavor. You can certainly use natural cocoa in a pinch. Use a quality brand!
- Eggs: One large egg and two egg yolks are the ideal combination for this chocolate pastry cream.
- Flour and cornstarch: These two work together, along with the eggs, to thicken the chocolate pastry cream.
- Chocolate: I generally use semisweet or bittersweet, but I can tell you from recent experience that using half unsweetened and half milk chocolate renders an outstanding result! Play with different chocolate combinations to see what you like!
- Vanilla: Just a little vanilla to complement the chocolate and further enhance the flavor.
Here are my best tips for making chocolate pastry cream:
- Line a baking pan with plastic wrap. Once the pastry cream is made, you will pour it into the plastic wrap and wrap it up while the pastry cream is still hot. Alternatively, you can have a heat proof bowl ready and a piece of plastic wrap to place on the surface of the pastry cream once it is made. You want to wrap it up while it is still hot to avoid a skin from developing, which happens when milk is cooked. (You may have experienced this with homemade puddings.)
- While heating up the milk, sugar and cocoa powder, in a heat proof bowl, whisk together the egg, yolks, remaining half the sugar, the flour and the cornstarch. I don’t mean to just whisk them. I mean to whisk them vigorously for a couple minutes so the mixture becomes fluffy and pale in color. If your arm gets tired, take a short break to stir the milk/sugar/cocoa powder mixture to ensure that the sugar gets dissolved.
- Once the milk/sugar/cocoa powder mixture comes to a simmer, turn the heat off and pour about half of the milk mixture into the egg mixture while whisking constantly. Make sure to have the heat proof bowl on a non-slip surface or have someone hold the bowl, as you need to whisk with one hand while pouring the heated milk mixture with the other hand. If you do not whisk as you pour the milk, you will end up with scrambled eggs. This step is called tempering.
- Pour the tempered egg mixture back into the saucepan with the remaining milk mixture. Over a medium-low heat, whisk constantly. The mixture will start to thicken. Once the mixture starts to boil (which should only take a minute or so), set a timer for exactly two minutes. Two minutes is the magic number to ensure the eggs are properly set and the enzymes in the cornstarch are properly activated. Keep cooking and whisking non-stop for the two minutes. I suggest wearing an oven mitt to protect your hand from the heat of the stovetop as you whisk. At the two minute mark, turn the heat off and pour in the chopped chocolate and vanilla. Whisk until the chocolate is fully melted and the mixture is smooth. Immediately pour the cooked chocolate pastry cream onto the prepared plastic wrap and, while it is still hot, wrap the plastic wrap all over it. Let it cool on a wire rack for 30-45 minutes and then store it in the refrigerator.
2. Make the Graham Cracker Cake
One of my favorite vanilla sponge cake recipes for Boston cream pie is from the Preppy Kitchen. I adapted his recipe for this graham cracker cake recipe. This cake is actually quite simple and comes together in just a few quick steps:
- Prepare the 8-inch round baking pan by spraying it with non-stick spray and lining it with a parchment round. Then give the parchment a spritz of non-stick baking spray.
- Whisk all the dry ingredients together in a small bowl and set it aside.
- In an electric mixer, whisk together the eggs and the sugar for at least 5 minutes on a medium-high speed. Then increase the speed to high for an additional 4-5 minutes.
- While the eggs and sugar are whisking, in a small saucepan over a medium-low flame, heat up the milk and the butter, just until it comes to a simmer. Give it a few swirls every now and then to make sure the butter is fully melted before the milk really heats up.
- Reduce the mixer to the lowest speed and mix in the dry ingredients, immediately followed by the heated milk and butter. Just mix until it is all combined and do not overmix.
- Pour the batter immediately into the prepared baking pan and bake for about 35 minutes.
- Cool on a wire rack for 15 minutes, then use a metal spatula to release the cake from the sides of the pan. Invert onto a wire rack and cool completely.
3. Prepare the Cake and Start Assembling
Once the cake has cooled, keep it upside down and slice it in half to create two layers. I highly recommend using a ruler to ensure even halves. Start by making a slight indentation with a aerated knife. Keeping the knife level, turn the cake without impressing the knife, just to mark the outside edge of the cake. Once you make it around, apply some pressure to the knife and keep turning the cake. To make sure you put the layers back in the same place, insert two toothpicks in the sides of both layers, one above the other, with the cut layer between the two toothpicks.
You will need to beat the pastry cream which you can do by hand, but it is much easier to use a stand or hand mixer. You can just spread the pastry cream on the exposed part of the cake. Alternatively, you can pipe it in a decorative fashion along the edges, as shown in the accompanying video. Place the other half of cake, lining up the toothpicks, over the pastry cream and refrigerate the cake for up to one day.
4. Make the Marshmallow Creme Frosting
This is the same Marshmallow Creme Frosting I use in my Chocolate Cake with Marshmallow Frosting (copycat Entenmann’s Marshmallow Devil’s Food Iced Cake).
The Marshmallow Creme Frosting is simple to make, but does require a small bit of precision because you want to make sure you heat the egg whites up to the proper temperature. All you do is fill a pot with about an inch of water and bring it to a boil. Using the bowl from your electric mixer, add all the ingredients except for the vanilla. Reduce the heat so the water is at a simmer. Place the mixing bowl on top of the pot and whisk all the ingredients together until it reaches 160° F. Then remove the bowl from the pot, place it in the mixer and whisk on medium-high until the mixture becomes stiff, meaning that a stiff peak holds when you lift the whisk out of the mixture. Toss in the vanilla and whisk until combined.
5. Torch the Marshmallow Creme Frosting
I like to pipe the Marshmallow Creme Frosting, but you can just as easily spread it on top, creating some waves and texture. Then, the fun part. Use a kitchen torch on a low setting to brown the top of the frosting. My torch of choice these days is from Jo Chef. (And this is just my opinion, although they did send me a free one to try and I fell in love with it.) They include the butane when you purchase it, and it is a very simple torch to use. If you’re in the market for a kitchen torch, I suggest you check it out!
Frequently Asked Questions About Making S'Mores Boston Cream Pie
Can I make S’Mores Boston Cream Pie in advance?
Yes. You can make the chocolate pastry cream and the cake a day before serving, storing them both in the refrigerator. You can also make the completed cake in advance, but just be sure to have enough space in the refrigerator because you do not want anything to fall on the gorgeously torched frosting.
What type of chocolate is best in chocolate pastry cream?
Half unsweetened and half milk chocolate is a wonderful combination. You can also use semi-sweet or bittersweet, or any combination of any of these chocolates. Just be sure to use a high quality chocolate brand.
S'Mores Boston Cream Pie
- 475 grams whole milk (1¾ cups plus 3 Tablespoons)
- 125 grams sugar (⅔ cup less 2 teaspoons)
- 1 Tablespoon Dutch process cocoa
- 1 large egg
- 2 large egg yolks
- 25 grams flour (3 Tablespoons)
- 25 grams cornstarch (3 Tablespoons plus 1 teaspoon)
- 142 grams bittersweet or semi-sweet chocolate*, finely chopped (5 ounces)
- ½ teaspoon vanilla extract
- 100 grams graham cracker crumbs (¾ cup)
- 60 grams all purpose flour (½ cup)
- 1¼ teaspoons baking powder
- ¼ teaspoon flaky sea salt
- 1 Tablespoon vanilla extract
- 2 large eggs (at room temperature)
- 200 grams sugar (1 cup)
- 120 grams whole milk (½ cup)
- 71 grams unsalted butter (5 Tablespoons)
Marshmallow Crème Frosting:
- 2 large egg whites
- 100 grams sugar (½ cup)
- 55 grams light corn syrup (2 Tablespoons plus 2 teaspoons)
- ¼ teaspoon cream of tartar
- ⅛ teaspoon salt
- 2 teaspoons vanilla
- Line a baking sheet with a long piece of plastic wrap. Alternatively, set aside a heat proof bowl and a piece of plastic wrap.
- In a medium saucepan, combine the milk, half the sugar (approximately 63 grams), and the cocoa powder. Over a medium heat, bring the mixture to a simmer, stirring occasionally.
- In a heatproof bowl, whisk together the remaining sugar, eggs, egg yolks, flour and cornstarch, until it is thick and pale in color.
- Whisking constantly, pour approximately one-half of the heated milk mixture into the egg mixture. Pour the tempered egg mixture back into the pan with the rest of the milk. Heat over medium heat, whisking constantly. Once the mixture start to boil, set a timer for 2 minutes and continue whisking constantly. At the two minute mark, remove the pan from the heat and immediately add the chocolate and the vanilla, whisking until the chocolate is fully melted and mixed in. If the mixture has some scrambled eggs in it, push it through a strainer onto the prepared baking sheet lined with plastic wrap. If the mixture appears smooth, there is no need to strain it. Immediately cover the pastry cream entirely with the plastic wrap and allow it to come to room temperature before using. The pastry cream can be made up to three days ahead and stored in the refrigerator until you are ready to use it. (You can use it directly from the refrigerator.)
- Preheat the oven to 350° F. Grease an 8-inch round cake pan with non-stick spray. Line the bottom with parchment paper and spray the bottom of the parchment paper with non-stick spray.
- In a small mixing bowl, whisk together the graham cracker crumbs, flour, baking powder and salt. Set aside.
- Place the eggs and the sugar in the mixing bowl of a stand mixer. With the whisk attachment, beat the eggs and sugar on medium speed for 5 minutes, then increase to high speed for an additional 4-5 minutes. The mixture will be pale and thick and will hold its shape for at least several seconds when dropped on itself.
- While the eggs and sugar are whisking, combine the milk and butter in small saucepan and heat over low heat, stirring occasionally to help the butter melt, just until the mixture comes to a simmer. Turn the heat off and stir in the vanilla.
- Set the mixer to the lowest speed and add the dry ingredients, just until almost fully combined. With the mixer still running on the lowest speed, slowly pour the hot milk mixture into the batter and continue mixing just until all ingredients are fully combined. Use a spatula to scape the sides of the bowl and to ensure the batter is fully mixed. Pour the batter into the prepared pan.
- Bake for 33-36 minutes. The cake should be lightly brown on top and a toothpick inserted in the center should come out clean. Allow the cake to cool in the pan for 15 minutes before using a metal spatula or knife to release it from the sides of the pan. Invert the cake onto a wire rack to cool completely.
Marshmallow Creme Frosting
- Fill a medium size pot about one-third with water. Place the pot on a burner over medium-low heat. In the metal bowl of a stand mixer, combine all ingredients except for the vanilla. Place the bowl over the pot of water. The water should not touch the bottom of the mixing bowl.
- Constantly whisk the mixture until it reaches 160° F. If using pasteurized egg whites, you can go to just 140° F. Do not stop whisking, as you do not want scrambled egg whites. Once the mixture reaches the correct temperature, immediately remove the mixing bowl from the heat and insert it onto the mixer with the whisk attachment. Whisk at medium-high speed until stiff peaks form. (Start mixing immediately. The mixture will cool as it is whipped.) Add vanilla and whisk an additional 30 seconds until fully incorporated.
- Slice the cake in half so you end up with two layers. Set aside the top half (which was on the bottom of the pan before you inverted it to cool).
- Place the chocolate pastry cream into a mixer (or use a hand mixer) to beat the pastry cream for a minute or two. Spread the pastry cream evenly on top of the bottom layer of the cake. Place the other half of the cake on top of the pastry cream.
- Pipe or spread the marshmallow creme frosting on top of the cake. If desired, carefully use a kitchen torch to brown the frosting.