Melt the chocolate slowly in a small saucepan, turn off the heat and dissolve the butter in it.
Beat the eggs with sugar and vanilla sugar to a light, frothy mass and fold in the chocolate butter. Then fold in the sifted flour and pour into the greased molds (e.g. for muffins).
Bake in a preheated oven at 180 ° C for about 15 minutes, turn out of the molds and sprinkle with cocoa powder.