Step 1

In a medium pot, whisk together the sugar, brown sugar, cocoa powder, salt, and cornstarch until no lumps remain. Add the eggs yolks and about 1/3 cup of the milk, and stir to create a thick, smooth, paste.

Step 2

Place the pot over medium heat, and gradually whisk in the remaining milk. Cook, stirring constantly, until thick and smooth - 5 to 10 minutes. Be cautious not to scorch the pudding.

Step 3

Remove from the heat and add the butter and vanilla. Stir until melted.

Step 4

Pour into a bowl with a lid and place a sheet of plastic wrap directly on the top of the pudding to prevent a skin from developing. Place the lid on the bowl and store in the refrigerator for at least 4 hours to allow it to thicken more. Served chilled.