1. Add the butter and confectioners‘ sugar to a large bowl and mix until light and fluffy. You might have to scrape down the bowl several times. Add the egg yolks, vanilla extract, and lemon zest and mix in well. Mix the flour with the salt and add to the bowl – mix/knead until just combined. Shape a ball (the dough will be very sticky) and wrap in plastic wrap and place in the fridge for at least 2 hours.

2. Preheat the oven to 200°C (390°F). Line a baking sheet with baking parchment and set aside. Mix the jam/jelly with a spoon to get it softer. If you don’t like the seeds of raspberry jam, for example, remove them before you use it (pressing through a sieve).

3. Take the dough out of the fridge and let it warm up a bit. Make about 25 walnut-sized balls out of the dough and place them on the baking sheet. Use the back end of a wooden spoon and press a little depression in each ball and fill with jam or jelly. Bake the cookies for about 12-14 minutes. Take them out of the oven and let them cool down on a wire rack. Dust with some confectioners‘ sugar while they are cooling if you like (optional).