For the dough, melt the butter, slightly cool, add sour cream and stir everything with a mixer. Add sugar, vanilla sugar and whisk the mixture well. Sift flour through a sieve together with a baking powder, gradually (portionwise) add to the prepared mixture and knead soft dough. Mince the dough. Lay the formed dough "noodles" evenly on a baking sheet covered with a baking parchment, and place in the oven preheated to 180°C. Bake until brown for 15-20 minutes, and then cool. Crumble the baked cookies with hands. For cream, whip the boiled condensed milk with butter until smooth and add the cookie crumbs, leaving a little for sprinkling. Stir and put the resulting mass on an oiled dish heaped. Refrigerate for at least 2 hours, then take it out, leave to proof for 15 minutes at room temperature, sprinkle with the remaining crumbs, optionally top with melted chocolate and serve.