Fill a large bowl half way with ice. Pour cold water over the ice so that the bowl is no more than ⅔ high. Place a clean bowl on top of the water bath. Place a strainer over the empty bowl.
If using a vanilla bean, slice it with a paring knife down the middle lengthwise and scrape the seeds out with the back of your knife. Place the pod and the seeds into a 2 or 3 quart saucepan. (If you are using vanilla bean paste or vanilla, add whichever you are using to the saucepan instead.) Add the cinnamon sticks, milk, cream and half the sugar. (You can eyeball half the sugar.) Over low to medium heat, stir the mixture occasionally to ensure the sugar dissolves. Heat to a simmer.
While the liquid heats up, whisk the egg yolks with the remaining sugar. You want to whisk it until the mixture turns pale yellow, becomes thick, and forms a ribbon when dripped on itself. (You can use an electric mixer with the whisk attachment if you are feeling lazy.)
Once the liquid mixture comes to a simmer, turn the heat off and let it sit for a minute or two. With the bowl holding the egg/sugar mixture secure on the counter (if no one is around to hold it, place it on a rubber mat or wet a dishtowel and wrap it around the base of the bowl), slowly pour the heated liquid mixture into the eggs, whisking constantly. Once fully incorporated, pour the contents of the bowl back into the saucepan. Over a medium-low heat, stir the mixture constantly with a wooden spoon until it reaches 185°F or a line holds when you drag your finger across the back of the wooden spoon. (It should only take a minute or two to reach the correct temperature.)
Immediately remove the saucepan from the heat and pour the cooked mixture through the strainer into the empty bowl sitting in the ice water bath. Lift strainer and discard the cinnamon sticks. (You can rinse off the vanilla bean in cold water and let it air dry completely for at least 24 hours. Save it for later use, such as to make vanilla sugar.) Stir in the ground cinnamon. It will not fully incorporate, but you want to mix it in enough to hydrate it. Stir the mixture as it sits in the ice bath every 2 to 3 minutes until the mixture has completely cooled. This usually takes about 10 minutes.
Pour into a container. Cover with plastic wrap directly over (touching) the mixture. Cover and place in refrigerator for 4-24 hours.
Follow your ice cream manufacturer’s directions to churn the ice cream. Transfer the ice cream to a freezer container. Cover with a piece of parchment paper or plastic wrap directly on the surface. Cover container and freeze.