In a mixing bowl, combine quark (or yogurt), cream cheese, sugar, vanilla extract, eggs, melted butter, and cornstarch.
Mix until smooth and creamy.
Pour the filling into the prepared crust and smooth the top.
Crumble the remaining 1/3 of the dough over the top of the filling.
Bake for 50 minutes.
Let the cheesecake cool completely, then chill in the fridge before serving.