This delicious cheesecake using yogurt or quark with chocolate streusel is a nice addition to your cheese cake recipes.
If using yogurt place a clean cloth in a strainer place over a large bowl. Spoon the yogurt into it, fold the cloth over the top, add a small plate and a heavy can or glass of water on top for a weight. Let the liquid drip into the bowl for about an hour or more. Then use in the filling. This is called yogurt cheese.If you quark, use it straight from the package.
Mix the first four ingredients for the crust until fine crumbs form. Add egg and mix again until the dough comes together in larger crumbs, like streusel. If still too dry, you may add a teaspoon or two of water.
Press 2/3 of the crust into a 10 inch buttered spring form pan.
Reserve the rest for streusel topping.
Preheat oven to 380°F.
Beat the 3 egg whites until foamy. Drizzle in ½ cup sugar and 1/8 teaspoon salt and beat until soft peaks form. Do not overbeat.
In a separate bowl, beat the egg yolks with 2 tablespoons of sugar and the vanilla extract; add the yogurt cheese or quark and lemon zest and beat until smooth.
Sift the cornstarch over the filling mixture and mix well.
Fold in the egg whites.
Pour the filling mixture over the crust.
Top with the remaining streusel.
Bake for 30 minutes, then reduce the temperature to 350°F and bake for 15 minutes, or until set in the middle.