Preheat stove to 225 °C. Mix salt, baking powder, flour and sugar in a baking bowl, work in butter with a kitchen knife until small crumbs are formed. Quickly knead in the sour cream with your hands. Roll out dough and cut out cookies with a round cookie cutter. Brush with egg and bake for about 10 minutes.
For a substantial breakfast or brunch. Delicious and classic with strawberry jam.