For the baked cheesecake, first melt the butter and let it cool. In the meantime, crumble the butter cookies in a freezer bag with a meat mallet or in a blitz chopper. Mix butter with butter cookies.
Line a springform pan with baking paper and grease the sides. Spread the cookie mixture over the bottom and around the edges of the pan and press down well. Place in the refrigerator for at least 20 minutes.
Preheat the oven to 180 °C top/bottom heat.
Separate the eggs. Beat egg whites with salt until stiff. Mix mascarpone, yogurt and cornstarch until no lumps remain. Stir in sugar, vanilla sugar and lemon zest. Stir in egg yolks. Finally, gently fold in the beaten egg whites.
Spread the mixture in the pan and bake for about 40 minutes. Do not open the oven door during this time. The mixture will still be a little soft at the end. Let baked cheesecake cool completely before removing from the pan.
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