Syrup:
13g (about 0.5 oz) butter
25g (about 0.9 oz) sugar
37g (about 1.3 oz) milk
Dough:
syrup
200g (about 1.4 cups) flour
4 tablespoons powdered sugar
100g (about 3.5 oz) butter
1 egg yolk
For the syrup: In a small saucepan, combine the butter and sugar, bringing it to a boil. Add the hot milk and cook until the syrup thickens. Allow it to cool to room temperature.
For the dough: Mix the flour, powdered sugar, butter, and egg yolk, then add the cooled syrup. Knead the dough well. Place the dough in the refrigerator for 30 minutes.
Roll out the dough thinly, dusting with flour to prevent sticking. Cut out cookies, making half of them whole and the other half with a hole in the center. Place them on a baking sheet lined with parchment paper and bake at 200 degrees Celsius (about 400 degrees Fahrenheit) for approximately 10-15 minutes.
Once the cookies have cooled, spread thick jam on the whole cookies and top them with the ones that have a hole. Dust with powdered sugar.