Coarsely chop the dark chocolate. Melt butter and chocolate in a saucepan over low heat while stirring, remove from the heat and pour into a mixing bowl. Add sugar, vanillin sugar, salt, eggs, flour and baking powder. Mix to a smooth dough with the whisks of the hand mixer. Place paper sleeves in the recesses of a muffin tray (12 recesses).
Pour in the dough and bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 20 minutes. Remove the muffins from the oven and let them cool down on a cake rack. Sift icing sugar into a bowl. Add the egg whites and whisk smooth with the whisk of the hand mixer. Add lemon juice to make a thick icing. Remove 2 tablespoons of the icing and put it into a freezer bag. Colour the remaining icing pink with food colouring. Add the pink icing to the muffins with a tablespoon and let it dry for about 5 minutes. Cut a small corner from the freezer bag. For the butterflies, cut the bark chocolate in half first crosswise, then lengthwise.
Remove 2 tablespoons of the icing and put it into a freezer bag. Colour the remaining icing pink with food colouring. Add the pink icing to the muffins with a tablespoon and let it dry for about 5 minutes. Cut a small corner from the freezer bag. For the butterflies, cut the bark chocolate in half first crosswise, then lengthwise. Press 2 biscuits each as wings into the icing. Use the white icing to paint small dots on the icing and biscuits and place the chocolate between the biscuits