Pie Dough. Remove pie dough from the refrigerator and let it rest at room temperature for approximately 5 minutes. On a lightly floured surface, roll out the dough so that there is approximately a 1 inch overhang over the sides of the pie dish. Trim and crimp the edges. Place pie dish with the prepared pie dough in it into the refrigerator or freezer while you make the brownie filling.
Brownie Filling. Preheat oven to 350°F.
In an electric mixer with either the whisk or paddle attachment, whisk/beat eggs on a medium-high speed. Once the eggs start to get foamy, increase the mixer to high and add the white sugar (not the brown sugar) slowly, a little bit at a time. Once all the sugar has been added, allow the eggs and sugar to continue whisking/beating for approximately 5-10 minutes until it is thick, pale yellow, airy, and forms a ribbon when dropped on itself.
Meanwhile, place the marshmallows in a medium saucepan over the lowest heat. As they start to melt, stir them. They will clump into a sticky ball. Add the butter and chocolate. Stir occasionally until all ingredients are fully melted. (Don’t sweat it if there are few unmelted marshmallows.) Remove from heat. Stir in the brown sugar, cocoa powder, espresso powder, and vanilla. Transfer to a large mixing bowl and set aside for a couple of minutes to make sure the mixture cools completely.
In a small bowl, whisk together the rye flour and salt.
With a spatula, gently fold in the beaten eggs to the chocolate mixture. Fold (do not mix) the batter until the eggs are fully incorporated.
Gently fold in the flour and salt just until all the flour is fully absorbed.
Pour batter into cold pie dough. Bake for 45-50 minutes, just until a toothpick inserted in the middle comes out clean. Cool completely on a wire rack.
Topping. Place the refrigerator cold ganache in a cold mixing bowl. With an electric mixer or by hand with a whisk, whisk the ganache until stiff peaks are formed. Spread on top of cooled brownie pie, or pipe it decoratively on top.