Beat the egg yolks with the vanilla pulp, sugar and salt until frothy. Gradually beat in the softened butter. Mix in the flour and baking powder and knead everything into a smooth dough. Shape into round sticks and refrigerate for two hours.
Cut the stiff dough sticks into 1/2 cm thick slices and place them on two baking sheets lined with baking paper. Mix the whole egg with 1 tablespoon of water and coat the biscuits thickly with it. Then score the surface with a knife in a grid shape and sprinkle with sugar sugar.
Preheat the oven to 180 ° (or 160 ° convection) and bake the biscuits until golden brown for about 12 minutes.