Cream butter, add sugar by spoonfuls and eggs one at a time. Fold in flour, Kölln instant flakes and baking powder. Grease a loaf pan, and line the bottom with parchment paper and grease. Pour in the batter and smooth it out. Bake at 190 °C , medium rack for about 60 minutes. Turn the hot cake out onto a baking rack and remove the paper. Mix the powdered sugar with the orange juice and the juice of one lemon and spread it on the cake with a brush until the liquid is used up.
Good luck!