In a bowl, beat the unsalted butter and powdered sugar together until light and fluffy, about 2-3 minutes. In another bowl, mix the egg yolks with the vanilla extract until combined. Preheat the oven to 340°F (170°C).

Add the egg yolk mixture to the butter mixture and beat for 30 seconds to 1 minute until well combined. Add the flour, salt, and baking powder, then mix for about 1 minute until just combined. If the dough is too dry, add a little water.

The dough is ready when it comes together and doesn't stick to your hands. Shape the dough into pieces weighing 25-27 grams each. If you like, you can add chocolate chips inside as a filling.