Place a bowl of chocolate pieces (or chocolate chips) in a water bath. After it has melted, let it cool. Whisk the butter, sugar and vanilla extract and add the melted chocolate. Then, whisk one egg at a time into the mixture. Finally, add the flour with cocoa and baking powder. When the dough is nice and smooth, place it in the fridge (preferably overnight). The next day, preheat the oven to 380F and bake small balls of the dough covered in granulated sugar first, then in powdered sugar, on a lined cookie sheet for about 10-12 minutes. Let them cool after they are done.