Chop 600 g chocolate. Cut butter into pieces. Melt butter and chocolate in a wide saucepan while stirring over 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, cocoa, baking powder and gingerbread spice and fold into the mixture quickly.
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 about 50 triangles. Chop 50 g chocolate and melt over a warm water bath. Put the chocolate in a piping bag with a small perforated spout and distribute in strips over the triangles.
Sprinkle with coloured sugar.