Beat softened butter and sugar until creamy.

Add egg yolks one by one and vanilla extract. Combine.

Lastly, add flour and mix just until combined.

Wrap the pastry in film and refrigerate for an hour

Extend pastry until 3mm thick. Cut an even amount of cookies and cut a smaller shape in the center of half the cookies.

Bake at 175°C for 7 minutes. Let cool.

Make cookie sandwiches with one whole cookie, jam, and a cutout cookie.