Beat eggs, sugar, vanilla and salt until light and fluffy.
Add sour cream and softened butter and mix very briefly.
Mix flour with baking powder, add it in batches to the egg sugar mixture and knead briefly and quickly to form a soft, slightly sticky dough.
Place the dough in a freezer bag, press it flat and put it in the fridge for 1 hour.
On a floured work surface, quickly shape the dough into 12 balls (72 g each in my case) and cut each ball in half using a pizza knife or a sharp knife.
Spread the cookies in the shape of ball halves, cut side down, on a floured cutting board and place them in the freezer for 15 minutes.
Spread the cookies out again, cut side down, on a baking sheet lined with baking paper with plenty of space between them and bake in a preheated oven at 356 °F (180 °C) for approx. 15 minutes.
Leave the cookies to cool until warm and make a hollow in the flat side of each cookie using a teaspoon or small knife.
Leave the cookies to cool completely.
Finely crumble the cut-out cookie scraps.