In a large saucepan, bring 1 1/2 c. of the milk, sugar, cocoa, chopped chocolate, and salt to a boil over medium high heat.
In a large bowl whisk the remaining 1/2 cup of milk, cornstarch, salt, egg yolks, and vanilla in a bowl. Slowly whisk the hot milk into the egg mixture. You don't want the eggs to curdle.
Pour the mixture back into the saucepan and cook over medium-high heat constantly whisking until the pudding comes to a boil. Reduce the heat to a simmer, and continue whisking until thick, 2 or 3 minutes more.
Remove from the heat and stir in the reduced stout.
Pour into a container and allow to cool. Once cooled, refrigerate until ready to assemble cups.