- In a bowl, mix the butter and powdered sugar (you can use a mixer, you can use a regular whisk). Next, add vanilla sugar and an egg white, mix and add flour.
- Knead the dough: it should be soft and homogeneous.
- Transfer to a piping bag (I have a "Closed star" tip) and set the cookies on a baking sheet lined with parchment paper.
- In the center of the cookies make a small deepening, and lay out the filling (jam mixed with starch).
- Bake the cookies in a preheated oven at 392F (200C) for 12-15 minutes.