Place the cocoa, cornstarch and water in a heavy-bottomed sauce pan over medium heat. Stir everything together; don't worry about a few small lumps., Whisk in the sweetened condensed milk and egg yolks. Since the mixture is barely warm, there's no need to worry about the yolks cooking., Cook the chocolate pudding for 4 to 5 minutes, or until it's thick and creamy. Remove it from the heat and immediately stir in the butter, vanilla and espresso powder. The chocolate pudding will become very smooth and glossy., If desired, press the chocolate pudding through a sieve to remove any lumps. Place a piece of plastic wrap directly on top of the chocolate pudding to prevent a skin from forming, and chill for several hours., Portion into individual ramekins, coupes, or wine glasses for serving. Garnish with homemade whipped cream and chocolate shavings, if desired. The cooked chocolate pudding can also be transferred to a pre-baked 9" pie shell and chilled until firm for a delightfully silky, easy chocolate cream pie. Store leftover chocolate pudding in an airtight container in the refrigerator for up to several days.