Pflaumen-Streusel-Käsekuchen (plum streusel cheesecake)

Method

1. Rub the cold butter into the flour, sugar, baking powder and salt until it looks like coarse crumbs, then work in the egg just until a dough forms. Press into the base of a 26 cm springform, about 2 cm up the sides, and chill for 20 minutes.
2. Make the streusel: rub the cold butter into the flour, sugar and cinnamon with your fingertips until it forms coarse, pea-sized crumbs. Chill until needed; warm streusel melts into a solid sheet instead of staying crumbly.
3. Beat the quark, sugar, eggs, cornstarch and vanilla together until smooth, then pour over the chilled base.
4. Press the plum halves cut-side down into the filling, spacing them evenly, then scatter the streusel over the top in an even layer.
5. Bake at 175°C for about 50 minutes, until the streusel is solidly golden brown and a skewer inserted into the filling between two plums comes out with only a little moist custard clinging to it.
6. Cool in the tin for 20 minutes, then release the sides and cool completely on a rack before slicing; it cuts cleanest once fully cool, though it is very good slightly warm too.

Notes

• Keep the streusel cold until it goes into the oven. Warm butter in a streusel mixture melts and spreads into a single crust rather than baking into distinct crumbs, and there is no fixing it once it has happened.
• This bakes firmer and cakier than a water-bath cheesecake on purpose. The higher, faster heat is what browns the streusel; a low, slow bake would leave the topping pale and soft.
• Do not skip draining the quark. A wet quark combined with juicy plums gives a filling that stays loose in the centre no matter how long it bakes.
• It keeps for 3 days at room temperature under a cake dome, or 5 days in the fridge, though the streusel softens somewhat once refrigerated.

Ingredient substitutions

• Plums can be halved apricots or quartered greengages in the same weight; firmer stone fruit holds its shape better through baking than very ripe fruit.
• Quark can be replaced with well-drained ricotta for a slightly grainier, sweeter filling.
• Ground cinnamon in the streusel is traditional but optional; leave it out for a plainer, more butter-forward crumble.
• For a nuttier streusel, replace 30 g of the flour with 30 g of finely chopped almonds or hazelnuts.