Beat eggs with the sugar. Melt the butter and add sour cream, flour, the egg-sugar mix and baking powder, stir.
Divide the dough into two parts. Add the cocoa powder to one of them and stir. Put the dough into a buttered baking mold in layers. Bake the cake in an oven at 340oF (170oC). for 50-60 minutes.
Sprinkle the cake with sugar powder and cut into slices before serving.
