Separate the egg yolks from the egg whites.
Beat the egg yolks with the 400g sugar and 1 packet vanilla sugar until the mixture is light and fluffy.
Grate the zest from the lemon.
Squeeze the juice from the lemon.
Add the lemon juice and lemon zest to the egg yolk mixture.
Add the 4 packs quark to the mixture.
Mix everything well until combined.
Melt the 125g butter and let it cool slightly so it's not hot.
Stir the melted butter into the quark mixture.
Add the 2 packets vanilla pudding powder to the mixture.
Beat the reserved egg whites with a pinch of salt until stiff peaks form.
Gently fold the stiff egg whites into the quark mixture.