Step 1

In a medium saucepan, heat the milk over medium heat until steaming (do not boil).

Step 2

In a medium bowl, whisk together the sugar, cornstarch, salt, and egg yolks until smooth and pale.

Step 3

Slowly pour about ½ cup of the hot milk into the egg mixture, whisking constantly to temper the eggs.

Step 4

Pour the tempered mixture into the saucepan and cook over medium heat, whisking constantly, until the mixture thickens to a pudding-like consistency, about 2 to 3 minutes.

Step 5

Remove from heat and whisk in the chopped chocolate, butter, and vanilla extract (plus rum or coffee liqueur, if using), stirring until smooth.

Step 6

Transfer the pastry cream to a bowl and press plastic wrap directly onto the surface to prevent a skin from forming.

Step 7

Refrigerate until fully chilled before using, 2 to 3 hours. Whisk before using to restore its creamy texture.