Beat the butter until frothy, gradually add the sugar - stir until the sugar dissolves.
Stir in egg yolks one at a time. Rub the lemon peel with the sugar cubes, then stir in the sugar cubes and add the flour.
Shape the dough into small balls and place on a greased baking sheet, press each ball lightly in the middle with your finger, fill the holes with ½ a spoonful of jam and brush with the rest of the egg yolk.
Scatter the almonds on top, bake the whole thing for about 12 minutes at 180 °.