Separate the egg yolks from the whites and cut the butter into small cubes, then mix half the sugar and the vanillin: beat with a whisk to get the cream and add six egg yolks.
Add the room temperature yoghurt, the grated lemon peel and stir so everything is well mixed. Whisk the 4 egg whites until stiff with a pinch of salt and sugar.
Add the egg whites to the butter and to the eggs, sift the flour and the baking powder and continue to mix with the ingredients.
Pour everything in a buttered and floured mould, and put the yoghurt cake in the oven at 180°. It will be ready to serve in about an hour.