Mix the first three ingredients together, then add the marzipan, plucked into small pieces, and stir until the pieces have dissolved. Mix the flour, nuts, almonds and baking powder together, add to the dough and stir.
Preheat the oven to 180 degrees circulating air. Line a baking sheet (approx. 20 by 28 cm) with baking paper and fill in the dough. Bake the cake for 20 minutes and then let it cool down. After cooling, cover the cake with a dark cake icing.