In a sauce pan over medium heat, whisk together the milk, sugar, cocoa, and cornstarch.

Turn the heat up to high and continue to whisk as the mixture starts to boil. Do not stop stirring. It takes about 6 minutes to bring to a boil.

Once boiling, continue whisking for another 2 minutes.

Remove pudding from heat. Stir in the vanilla.

Pudding can be eaten warm or chill in the refrigerator for up to 2 hours to be eaten later. When chilling, place plastic wrap on the surface if you want to avoid the "skin". Although the "skin" is fine to eat and can be stirred to loosen.

Top the pudding with fresh berries or whipped cream.