Remove the butter from the refrigerator in advance so that it is soft. Divide one egg into white and yolk. Beat the whites into a fluffy foam. Beat the yolk in a small bowl a little with a fork. Turn on the oven to preheat.
Beat the softened butter with a mixer with one egg, sour cream and sugar until the sugar is completely dissolved. Add baking powder, vanillin and flour in small parts, stirring until smooth. Knead the dough with your hands and put it in the refrigerator for 30-40 minutes.
While the dough is in the refrigerator, make the filling. Rub the cottage cheese with sugar. Add vanilla and a tablespoon of flour. Stir. Then carefully mix with the whipped egg white so that it does not settle.
Form the dough into small equal-sized balls. Roll each ball into a circle 3mm thick. Place the filling on one half of it, cover with the other half and lightly press down the corners. Repeat this with each ball of dough.
Line a baking sheet with parchment paper and grease with sunflower oil. Then place the juices and brush the top with yolk. Bake at 180°C for 15 minutes, then another 15 minutes at 160°C.
Sprinkle hot juices with powdered sugar. Serve with hot tea, coffee, cocoa or chilled juice, kefir.