1. Add cocoa powder, cornstarch, and salt to a large saucepan.
Whisk in cream, then the milk, stirring until there are no lumps (about 2 minutes). Add the egg yolks and brown sugar, then whisk to combine.
2. Bring to a boil over medium-high heat, whisking intermittently.
Reduce the heat to low and continue cooking and whisking until the pudding becomes thick and smooth (about 2 minutes).
3. Remove from the heat.
Add the chocolate, vanilla, and butter, stirring until the chocolate melts and the mixture is smooth and shiny.
4. If the pudding is lumpy, add an ounce of cream and whisk thoroughly to achieve a smooth, light surface — like ripples on a pond.
Transfer to a bowl or container.
5. If not using immediately, cover the surface with plastic wrap, pressing it gently against the pudding to prevent skin from forming, and refrigerate.
Be sure to remove the pudding from the fridge and allow it to reach room temperature an hour before applying it to your dessert pizza.
