For the bars: Chop the chocolate finely. Beat the butter until creamy and gradually beat in the sugar, vanilla sugar, rum extract, salt and egg. Add the chocolate, almonds, baking powder and sifted flour into the mixture. Spread the dough on a baking sheet lined with parchment paper. (Laying a multiply bent-over strips of aluminum foil before the dough.) Bake in preheated oven at 200°C (approximately 400°F) for about 20 minutes. Let cool.
For the topping: Cut the chocolate into pieces, place in a bowl and melt over a hot water bath, stirring occasionally. Spread the melted chocolate evenly over the cake. Draw wavy lines through the chocolate using a pie comb. Let chocolate harden. Make powdered sugar stars using an icing stencil over the chocolate topping. Cut into small pieces and serve.