Mix and beat the eggs with the powdered sugar, vanilla sugar to a creamy pale yellow batter.
In a separate small bowl mix the oil with the liqueur well and add it then to the sugar egg mix and combine.
Now add to the batter the flour and baking powder and mix it all well to a smooth batter.
Preheat the oven to 350° Fahrenheit/ 180° Celsius.
Grease your cake mold and fill in the batter. The greasing of the form prevents the cake to stick.
Bake your cake at 350° Fahrenheit/ 180° Celsius for 45 minutes.
Take out the cake and while it's still hot pour in more egg liqueur (about ½-1 cup) into the cake so that the cake soaks in the alcohol. Let it stand for 1 hour so that the liqueur may sink and disperse well into the cake.
Before serving turn the cake and spread powdered sugar to garnish on top.
In Germany, vanilla sugar is common. 1 packet makes almost 2 Teaspoon or 7 grams. You can also substitute vanilla sugar with plain vanilla extract and add about 2 teaspoon plain powdered sugar extra.