Cream together the butter & sugar until smooth; beat in the egg yolks. Blend in the dissolved hartshorn or ammonia and the rosewater, then the salt & spices. Stir in the flour and work until a ball of dough is formed. Knead gently until smooth, working in more flour if necessary.
Roll out the dough on a floured surface to a 1/4in thickness. With a floured butter knife, cut the dough into small squares or rectangles. Make decorative vent holes on the cakes by pricking with a fork, then place them on a baking sheet lined with parchment paper.
Bake in a preheated 300° F oven for 14-15 minutes until just done. Be sure that they do not brown on the bottom. Cool on a wire rack and store in an air-tight container.