1. Place the flour, butter, icing sugar and salt in a mixing bowl. Rub together until the mixture resembles breadcrumbs. Add the egg yolks and bring together to form a ball.
2. On a lightly floured surface, knead gently to form a smooth ball of dough. Wrap this in clingfilm and place in the fridge for at least 30 minutes.
3. Line two baking trays with parchment.
4. On a lightly floured surface, roll out the dough to 0.5cm thick. Using a 9cm square cutter, cut out 12 squares. You will need to re-roll the trimmings. Using a 4.5cm sure cutter, make a square hole in the middle of six of the large square biscuits. Place the biscuits on the prepared trays and put into the fridge to rest for 30 minutes.
5. Preheat your oven to 170°C/Gas 3.
6. Bake the biscuits for 12 to 14 minutes until pale and just beginning to colour, but cooked through. The biscuits will be soft whilst warm, so leave on the trays for a few minutes until they have set, then transfer them to a wire rack to cool.
7. Once cooled, take the whole biscuits and turn them upside down. Place a dollop of jam in the middle of each one. Spread it out a little, being careful not to go into the edges. Top each one with a biscuit with a hole in and gently push together.
Photography by Issy Crocker