Mix the flour, cornstarch, cocoa, baking powder and powdered sugar in a bowl. Dissolve the soluble coffee in a little hot water and add to the mixture with the egg yolk and butter. Knead quickly into a dough and put in the fridge for about 30 minutes. Then shape the dough into 2 cm long coffee beans. To do this, form a long roll from the dough and cut off pieces approx. 2 cm long. These are briefly rolled so that they look like larger coffee beans. Then you briefly press in the middle with a butter knife. Bake these coffee beans at 200 ° for about 10 to 12 minutes.
After cooling, decorate with white couverture. I always use a small freezer bag and cut off a small corner.