Cheesecake with Quark Cheese (German Käsekuchen)

German cheesecake is a traditional dessert consisting of a thin layer of shortcrust pastry that is topped with a creamy combination of quark cheese, eggs, and (occasionally) various fruits. Even though käsekuchen is often compared to the classic American cheesecake, the use of lightly acidic quark cheese results in a light, scrumptious treat that perfectly combines sweet and sour flavours. Usually served dusted with powdered sugar, käsekuchen is a classic German dessert that is commonly enjoyed as an everyday treat alongside coffee or tea.

Crust:
1½ cups all-purpose flour, unbleached
1 tsp. baking powder
pinch kosher salt
2 tsp. vanilla sugar or 1 tsp. pure vanilla extract
1 Tbsp. lemon rind, finely grated
¼ cup granulated sugar
6 Tbsp. butter
1 egg, beaten

Filling:
3 egg yolks
¾ cup granulated sugar
2 tsp. vanilla sugar or 1 tsp. pure vanilla extract
6 Tbsp. butter, room temperature
¾ cup heavy cream
2 cups quark or Greek yogurt
1½ tsp. cornstarch
3 egg whites
pinch kosher salt

For the Crust:
Combine sifted flour, baking powder, salt, lemon zest, sugar, and vanilla sugar or extract. Cut in the cold butter. Add the beaten egg and then use your hands to form into a dough. Wrap dough in plastic and chill in the fridge for an hour.

After the dough has chilled, form it into a disc and then roll it out on a floured surface. Shape dough into a disc again, and roll it out once or twice more. I found the dough very crumbly and hard to work with at first, but after I rolled it out twice, it became much easier to work with.

Roll dough out once more and then transfer to a prepared 9" springform pan. Use your fingers to press the dough so that it evenly covers the bottom and all the way up the sides of the pan.

For the Filling:
Beat the egg yolks, sugar, and vanilla sugar until pale. Add softened butter and continue beating until well combined. Add the heavy cream and beat again. Add quark (or Greek yogurt or puréed cottage cheese) and beat one more time until everything is thoroughly combined.

Beat egg whites and salt to stiff peaks in a separate bowl. Fold egg whites and sifted cornstarch into cheesecake batter.

Pour cheesecake batter into a 9" springform pan and bake on 300°F (150°C/130°C fan, Gas Mark 2) for about 60 minutes. (My cheesecake needed 70 minutes.) The cheesecake is done when the edges are browned and a toothpick comes out clean. The center of the cheesecake will be a bit wiggly and it will fall as it cools - that's normal.

Let the cheesecake cool on the counter for an hour and then several hours in the fridge. It's best to make this cheesecake the day before you want to serve it.