In a mixing bowl whisk together egg yolks and milk. (Any type of milk will work.) 2. In a saucepan, combine sugar, unsweetened cocoa powder, cornstarch, and salt.  3. Slowly pour the liquids over the dry ingredients, whisking well. 4. Heat the mixture until it begins to simmer. Whisk it constantly as it heats (this will prevent lumps). 5. Stir in chopped chocolate or chocolate chips (this gives it extra rich chocolate flavor). 6. Refrigerate until chilled. 7. Serve!