Preheat the oven to 180 degrees Celsius (356 degrees Fahrenheit) fan
Mix flour, baking powder, sugar, lemon zest, and vanilla sugar well
Rub the butter into the flour mixture until it is finely crumbled
Add vanilla essence and egg to bind the dough and knead briefly until it just comes together
Cut small pieces of about 5-6 g and roll them into small balls
Place the balls on a baking sheet lined with parchment paper and flatten them on top
Bake in the middle of the oven for about 12 minutes
Take them out and let them cool while you make the cold buttermilk soup