Makes 32 cookies
Prep time: 45 min. + chilling time
1. Beat egg yolk and butter and sugar until frothy using the whisk on an electric mixer. Add flour and lemon zest and mix at low speed. Wrap the dough in plastic wrap and chill for 1 hour.
2. Preheat oven to 160 °C (350° F, upper and lower heat).
3. Shape the dough into a roll on a lightly floured surface and then cut into 32 equal sized pieces. Flour your hands and then form each slice into a ball and place on a cookie sheet lined with baking parchment. Using your thumb or the handle on a cooking spoon, press an indentation into the middle of the cookie. Decorate the cookie by pressing granules of coarse sugar around the edge.
4. Bake the cookies about 8 min. on the second level in a preheated oven. Warm up the jam in a small pot and stir until smooth. Remove the cookies from the oven, carefully drop a dollop of jam in each indentation using a small spoon and then bake the cookies another 4 min.
5. Remove the cookies from the oven and put them on a rack to cool. Store in airtight tins.