Mix the flour, sugar, and salt together in a large bowl. Add the cold butter in pieces and rub into the flour mixture with your fingers until it is quite sandy.

Separate the yolk into a small bowl and break it up with a fork. Pour this into the sandy mixture and use the fork to mix the dough until it comes together into a ball. Separate the dough into three discs and wrap in plastic. Let cool in the fridge for an hour.

Preheat oven to 180 C / 350 F / gas mark 4

Roll out dough to be about half a cm thick and cut out cookies, trying not to work the dough too much when you re-roll, and leaving any dough that you are not using in the fridge. In half of the cookies, cut an additional hole (or three) to make the top.

Bake for 12-15 minutes, until golden.

Separate the tops from the bottoms. Dust powdered sugar over the tops. Smear a little jam (about half a teaspoon) on the bottom half and gently press the two parts together.

Cookies will keep for a week. Recipe adapted from Helvetic Kitchen. I have reduced the sugar to my liking.