Chopping chocolate. Cut butter into pieces. Melt both in a wide pot at low heat.
Beat the eggs, sugar and salt with the whisk of the hand mixer in a bowl for 3-4 minutes until creamy. Remove the liquid chocolate-butter mixture from the heat and immediately stir into the egg-sugar mixture.
Mix flour, baking powder, cocoa and gingerbread spice and fold into the mixture quickly. Chop the walnuts and fold in as well.
Grease the fat pan of the oven (approx. 33 x 39 cm). Add the dough, smooth it down and bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 20-25 minutes.
Take out the cake and let it cool down. Cut the cake into 48 pieces. Mix 200 g icing sugar and lemon juice to a thick icing. If necessary, remove part of the icing and colour with food paste.
Spread the rest of the glaze on the brownies or decorate the cubes with white or coloured glaze. Sprinkle with sugar pearls. Leave to dry. Decorate some brownies with remaining icing sugar using stencils.