Method of preparation

Freeze the butter, then grate it, and briefly put it back in the freezer. Mix flour, salt, baking powder in a bowl, then add butter and mix everything with a wooden spoon. You should get a mixture like sand. Add sour milk, but not all, save a tablespoon and a half. Knead the dough quickly, just enough to come together. Make a ball, wrap it in cellophane and put it in the freezer for at least 20 minutes. Use a rolling pin to roll out a disc no thinner than a finger and a half. Cut eight pieces with a knife, spread them with the rest of sour milk and arrange the pieces on a baking sheet covered with parchment paper. Place the tray in the heated oven and bake for about 20 minutes at 200-210 degrees.