Sift in a bowl the flour with the baking powder, salt and sugar. Add the pieces of softened butter and all good RUB. Beat the egg, gradually adding the yogurt. Pour the mixture into the flour. Mix well and kneading a smooth dough. Further, according to your desire or match rolls in ways that you prefer, or roll the rolls. Spread on a baking sheet. To grease with a yolk and bake until done.