Place the soft butter, eggs, smetana or sour cream, sugar, and vanilla sugar or extract in the bowl of the food processor. Mix until creamy.
In another bowl mix together the flour and the baking powder. Add them to the rest of the ingredients and mix well.
Turn the mixture on the lightly floured working surface and knead shortly to obtain a smooth dough. Wrap the dough in cling foil and refrigerate for one hour.
Preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit.
Divide the dough into four equal parts. Cut four large pieces of baking paper. Flour the rolling pin.
Flatten the first piece of dough on one piece of the baking paper to get a rough rectangle and then roll it to a rectangle of about 23x30 cm/ 9x12 inches. It works better if you have a small rolling pin, which you can hold in one hand, while you hold the baking paper with the other hand. If you only have a regular-sized rolling pin, maybe someone can hold the baking paper for you or you can fix it down with some tape.
Try to push the edges of the dough with a butter knife or your fingers in order to make them a bit neater and to prevent them from being thinner than the rest of the rectangle, so that they will not get excessively dry when baking. However, the edges do not have to be perfect, you can cut them straight and nicely after the cake has rested for the necessary two or three days.
Carefully place the dough on the baking tray and bake in the preheated oven for about 10 minutes or until the edges of the dough rectangle start to get brownish. Remove from the oven and let cool completely.
While the first cake layer is in the oven, roll the second one and so on until all four cake layers are baked.