Mix flour, butter, egg yolks, sugar, salt, dissolved cake yeast in warmed milk, sour cream, and cold milk to form the dough.

Divide the dough into 3 equal balls.

Refrigerate the dough balls for several hours or overnight.

Roll out each dough ball into a 42 by 62 cm rectangle.

Butter and flour a baking pan.

Place the first layer of dough in the prepared pan.

Prick the dough with a fork or toothpick.

Spread apricot or raspberry preserves evenly over the dough layer.

Mix ground walnuts with sugar.

Sprinkle the walnut-sugar mixture over the jam layer.

Place the second layer of dough on top.

Prick the dough with a fork or toothpick.

Spread the remaining jam and nuts over the second dough layer.

Place the third layer of dough on top.

Press down the edges of the cake.

Prick the top layer with a fork or toothpick.

Bake in a 400 degree oven for 30 minutes.

Let the cake cool completely.

Melt chocolate and mix with oil.

Spread the melted chocolate evenly onto the cooled cake.

Cut the cake into rectangles.

Arrange the rectangles on a serving platter to serve.