Cream butter and sugar for about 5 minutes. Stir in eggs, orange peel and salt. Mix flour, ground almonds and speculoos spice and add to the fat mass. Dissolve the salt of the deer horn in 1-2 teaspoons of water, also add to the bowl and knead everything into a smooth dough. Halve the dough and wrap each in cling film. Chill for about 30 minutes. Roll out one half of the dough on a floured work surface approx. 3 mm thin.
Sprinkle with half of the flaked almonds and roll over the dough again. Cut out rectangles (approx. 4.5 x 7 cm) with a sharp knife. Line 3 trays with baking paper. Place the biscuits on the baking trays and do the same with the remaining half of the dough. Bake the trays one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 12 minutes. Mix egg yolk and cream and spread the hot cookies immediately and let them cool down