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 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 lengthwise into 5 strips. Cut each strip into 9 isosceles triangles (6 x 8 x 8 cm) (nibble the leftovers.) Cut candy canes into pieces of approx. 5 cm and stick them as a trunk into each triangle.
Mix icing sugar with lemon juice and food paste to a firm glaze. Pour the icing into a piping bag with a fine piping nozzle and decorate the fir trees with it. Place sugar pearls and chocolate lentils on top.