Mix cornstarch with a ½ cup of cold Promise Land Midnight chocolate flavored milk to form a smooth paste.
In a heavy saucepan over medium heat, combine the sugar, cinnamon stick, and the remaining milk and bring to a simmer, stirring continuously (about 4-5 minutes).
Stir cornstarch mixture until smooth again and gradually pour it into the simmering chocolate milk, whisking rapidly. If you don’t mix it well before pouring it into the chocolate milk, it will form lumps. If you want, use a strainer to pour it into the saucepan. Bring to a boil, stirring constantly.
Stir in the vanilla. Cook for 5 more minutes, or until the mixture becomes thick, and it looks smooth like pudding. Just make sure to remove it from the heat before it starts to boil and form bubbles.
Remove the cinnamon stick and pour the chocolate milk pudding into the pie crust and smooth it out. Again, if you see some lumps in the mixture, pour it into the pie crust using a strainer with large holes (better safe than sorry). Let your pie cool down to room temperature, and after that, place in your fridge until it is completely set and firm to cut. This will take about 4 hours, but it is better to wait until the next day to slice it.
Sometimes the top surface of the filling (custard) doesn’t seem smooth enough. If this is the case, place the pie in the preheated 375F oven for 2-3 minutes. That will be enough time to smooth it out. Do not leave it in longer, because it will start to make bubbles and splatter all over your oven, and no one likes to clean ovens.
Just before serving, dust the pie with the cocoa powder. Enjoy with a cold glass of milk. You can also top it with whipping cream and some berries.