Coarsely chop the walnuts and chocolate, dice the butter. Melt the chocolate and butter in a hot water bath. Mix in sugar, salt and vanilla sugar. Stir in eggs bit by bit. Stir in flour and nuts.
Fill the dough into a square springform pan (24 x 24 cm) lined with baking paper, smooth it down. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 35-40 minutes. Take out, remove cake from the edge of the tin, let it cool down a little in the tin. Place in the refrigerator for about 1 hour, remove from the mould and cut into 3-4 cm cubes. Mix 50 g icing sugar and rum to a thin icing. Sprinkle brownies with it, let them dry. To decorate, mix 50 g icing sugar and lemon juice to a smooth glaze. Pour into a freezer bag, cut off a small corner. Decorate cookies with it.
Mix 50 g icing sugar and rum to a thin icing. Sprinkle brownies with it, let them dry. To decorate, mix 50 g icing sugar and lemon juice to a smooth glaze. Pour into a freezer bag, cut off a small corner. Decorate cookies with it. Sprinkle with delicately coloured and white sugar before the icing is dry