Beat the fat and sugar with the whisk of the hand mixer until white-creamy. Stir in the eggs one after the other. Mix flour and baking powder. Alternately fold flour and milk into fat egg mixture. Roughly chop the chocolate and fold into the dough.
Line the hollows of a muffin tray (12 hollows) with baking cups. Spread the dough in them. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 20 minutes. Remove and let cool on a cake rack.