In a small saucepan, add the milk, sugar, cocoa powder and vanilla extract. In a small bowl, whisk the cornstarch and water together, until no clumps remain.
Whisk in the cornstarch mixture into the saucepan and place it over medium heat. Stir it regularly, until it begins to simmer. Reduce it to low, and continue to mix for a further 5-6 minutes, until it has thickened. Remove the saucepan from the heat.
Let the pudding mixture cool to room temperature, before refrigerating it for at least an hour, until chilled.
Notes
TO STORE: Almond milk pudding should be stored in an airtight container in the refrigerator for up to one week. TO FREEZE: Place leftover pudding into freezer-safe containers for up to two months. The pudding must be thawed completely.