In a large bowl, combine the soft butter, marzipan raw mixture, sugar, and salt, mixing for about 2-3 minutes until smooth. Stir in the egg and flaky almonds. Sift the flour over the mixture and fold it in, partly stirring and partly kneading until fully combined.
Divide the dough in half and shape each portion into a roll approximately 35 cm long. Wrap each roll in foil and refrigerate for 2 hours. Cut the chilled rolls into 8 mm thick slices. Arrange the slices on a baking tray lined with baking paper. Bake in the center of a 175°C (347°F) oven for 10-15 minutes until golden.
Transfer the cookies to a cooling rack and let them cool completely. Melt the dark chocolate. Drizzle the cooled cookies with the melted chocolate in very fine lines.