Mix the butter with sugar and vanilla sugar until frothy. Then add the eggs one at a time. Mix the flour and cornstarch and also add the baking powder and salt. Gradually add to the egg mixture, preferably a tablespoon at a time. When all the ingredients are mixed and stirred, stir again for 3 minutes on the highest level with the mixer. Now add the egg liqueur and stir well. Grease and flour a loaf pan. Place in the preheated oven and bake at 180 degrees fan-assisted.
After baking, sprinkle with powdered sugar or cover with chocolate icing.