Using the paddle on your stand mixer (or a hand mixer), cream the butter, without making it fluffy, for about 1 minute. Then add both sugars, lemon peel and salt. Cream the sugar-butter mix until smooth (for 1 – 2 minutes).
Add the egg yolks and mix to combine very quickly, until the egg yolks are completely incorporated. Avoid overmixing.
Add the flour to the butter mixture, mix together on the lowest setting on your mixer. Or use a big mixing spoon until most of the flour has been incorporated with the butter mix. The dough should form big clumps.
Stop mixing, dust your hands lightly with flour and gently bring the dough together to form a smooth ball. Roll into a log, cover with cling wrap or baking paper and rest in the fridge for 30 minutes.
Roll the dough into small balls (approximately 15g each) place onto lined baking trays, leaving a gap for the biscuits to spread in the oven.
Use a rounded handle of a wooden spoon, or your thumb or finger to create a well in the middle of the biscuit.
Fill the hollow to the brim with Glühwein & Sour Cherry Jam using a small spoon or piping bag.
Bake in the oven for about 12-15 minutes until very lightly coloured.
Remove from the oven and leave to cool slightly before moving to a wire rack to cool completely.