Mix eggs, vanilla sugar and powdered sugar until frothy. Then slowly add the oil and egg liqueur and always stir vigorously. Sieve the baking powder and flour and add a spoonful at a time.
Grease a baking pan (loaf pan or sponge cake pan) and pour in the batter. Bake on the middle rack for about 60 - 90 minutes (it depends on the oven) until golden brown.