For the chocolate mini doughnuts, first melt the butter and let cool. Brush the mini doughnut tray with one third of the melted butter. Finely chop the chocolate.
Separate the eggs. Beat the egg whites with a pinch of salt until stiff. Mix the egg yolks with the remaining butter and the milk. Sift flour with baking powder and mix with salt and sugar. First fold the yolk mixture, then the beaten egg whites into the flour mixture. Finally, gently stir in the chocolate.
Heat the mini doughnut pan on the stove until the butter throws small bubbles. Place 3-4 tablespoons of batter in each indentation and bake the chocolate mini doughnuts for about 4-5 minutes on each side.