Step 1

In a small saucepan, combine 2 cups of milk, sugar, cocoa powder, and salt. Whisk until well combined. Cook over medium heat until very steam and just starting to simmer, stirring frequently.

Step 2

Meanwhile, in a large mixing bowl, whisk together the egg yolks, cornstarch, and remaining ¼ cup of milk. When the chocolate milk is hot, slowly whisk about a cup into the egg yolk mixture. (This tempers the eggs to keep them from scrambling.) Whisk in the remaining hot milk. Pour the mixture back into the saucepan.

Step 3

Place the saucepan back over medium heat and cook stirring constantly until the mixture bubbles. Continue cooking until thickened enough that the whisk leaves a trace when stirring in the mixture, about 3 minutes. (Temperature should be about 170F on an instant-read thermometer.) Remove from the heat and whisk in the butter and vanilla until melted and combined.

Step 4

Transfer the pudding to a bowl and press plastic wrap to the surface. Refrigerate until chilled, about 3 hours, or up to 4 days. Give it a good stir before dishing into serving bowls. Serve with whipped cream, if desired.