Mix Filling: In a large bowl, beat the quark cheese until smooth. Add the sugar, heavy cream, eggs, cornstarch, vanilla extract, lemon zest, and lemon juice. Mix until well combined and smooth.
2 lbs. Quark cheese, 1 cup Sugar, ½ cup Heavy Cream, 4 large Eggs, ¼ cup Cornstarch, 1 tbsp. Vanilla Extract, 1 Zest of Lemon, 1 tbsp. Lemon Juice