Grease the cake pan and dust it with flour.
Shake off the excess flour.
Whisk butter, powdered sugar, and vanilla sugar until white in a bowl.
Add the eggs one at a time, stirring constantly.
However, do not stir too much, so the batter does not curdle.
Sift flour and baking powder together and sift it into the batter along with grated lemon zest.
Pour the batter into the greased cake pan and bake in a preheated oven at 175 degrees Celsius (347 degrees Fahrenheit) (convection) for about 1 hour.
Let the cake rest in the pan for about 5 minutes before turning it out onto a wire rack to cool.