Knead a dough from the products and divide it into 2 balls. Wrap them in plastic wrap and put away in the freezer for about 2 hours.
For the cream mixture, beat the egg whites to snow. In another container, mix the yoghurt, sour cream, sugar, vanilla and flour. Beat well, so there's no lumps left in the flour. Stir the yoghurt mixture carefully with the egg whites.
Turn the oven up to 356°F (180 °C).
Put baking paper in a tray measuring about 8″ (20 cm) x 11 3/4″ (30 cm). Take the dough out of the freezer and grate 1 of the balls into the tray. Distribute the dough equally.
Pour on the cream mixture and even it out. Grate the other dough ball on top. Put in the oven and bake about 40-45 min. Let it cool fully and cut into pieces.