Preheat the oven to 180°C (350°F) and line a baking sheet with parchment paper.

Cream the butter and sugar together until light and fluffy.

Mix in the vanilla extract and egg yolk until fully combined.

Sift in the flour, baking powder, and salt, and mix until a soft dough forms.

Roll the dough out on a lightly floured surface to about 5 mm thickness.

Use a round cookie cutter to cut out pairs of cookies. For half the cookies, cut out a smaller shape in the center to create the top layer.

Place the cookies on the prepared baking sheet and bake for 10-12 minutes or until lightly golden.

Let the cookies cool completely, then spread a thin layer of fruit jam on the flat side of each whole cookie.

Top with the cut-out cookies to form a sandwich, gently pressing them together.