To prepare dough, sift wheat flour with baking soda and salt. Slightly whip 1 egg, 5 tbsp. sour cream, 80 g sugar and 100 g melted butter with a wire whisk. Combine the dry and liquid ingredients and knead dough. The given amount of flour is approximate. Roll out dough into 0.5 cm thick layer and cut circles no more than 10 cm in diameter using a mould. Grind 100 g cottage cheese in a blender, add sugar to taste, vanilla sugar, egg white, stir, then add 1 tbsp. sour cream and 1 tbsp. flour, and stir again. Put cottage cheese in the middle of the circle. Slightly press down. Place sochniki on the baking tray covered with a cooking sheet. Brush the surface with a yolk whipped with 1 tsp. milk. Bake in the oven preheated to 180 °C until done.