Preheat the oven to 180°C.
Melt the butter in the microwave for 30 seconds. If it is not completely melted, reheat for another 10 seconds until it is completely melted.
Place yoghurt, eggs, sugar, vanilla sugar, melted butter and lemon juice in a large container and mix until smooth.
Add the flour and baking powder and mix.
Butter a cake pan and then pour the cake batter into it.
Place in the oven for 45 minutes, check the baking by sticking a knife in the center of the cake, if it comes out dry, the cake is ready.
Zest the lemon with a grater on the cake before serving.