Soften the butter. Mix together the butter, 3 eggs, oil, salt (to taste), the soda and yoghurt. Add enough flour to thicken the mixture. (The Turks say, "until it has the texture of an ear lobe."). Roll out the dough and fold it over itself. Do this 5 times. Finally roll the dough into a ball and place it in a freezer. Remove from the freezer after 2 hours and allow to defrost. Roll with a rolling pin. Cut 40 small squares from the dough, and with your rolling pin, shape each one into a rectangle.

Partially cook the meat and grated onions in a small amount of butter. When the meat juice begins to disappear, let cool. Put a piece of meat in each rectangle of dough. Fold the small end over the other small end and press firmly to close the borek well. Dip in egg yolk and place in a buttered baking dish. Bake in a warm oven until the surface becomes golden brown.