In a saucepan, whisk together the sugar, cocoa powder, cornstarch, salt, and yolks until incorporated. Whisk in the milk until incorporated.

Place the pan over medium heat and cook. Whisk constantly. Let the mixture bubble for 5 minutes and then take it off the heat.

Stir in the butter, extract, and chocolate until incorporated. Strain the pudding and let cool with a piece of plastic wrap covering the top to prevent a skin from forming.