Sift the flour and freeze the butter.
To knead the dough, grate the ice-cold butter on a coarse grater, add sugar, 1 egg, previously sifted flour and baking powder. Knead the shortbread dough until elastic and roll into a ball.
Roll out the finished dough into a round layer no more than 5 mm thick and transfer to a baking dish greased with butter. Distribute the dough into the mold so that the sides are high enough - about 6 cm high.
Place the prepared filling on top of the dough so that the filling does not extend beyond the edges of the dough. Place the pie pan in an oven preheated to 180°C for 50 minutes.
Decorate the finished sour cream with grated chocolate or cocoa powder and serve, cutting into portions.