Mix the flour with baking powder, add softened butter, finely grated cheese, sour cream, egg, and salt. Knead the dough, roll it out to about 1.5 cm thickness, and cut out the scones. Transfer them to a baking sheet lined with parchment paper and brush with beaten egg yolk. You can sprinkle with additional grated cheese and bake at 200°C for about 20 minutes.