Himbeer-Käsekuchen (raspberry quark cheesecake)

Method

1. Rub the cold butter into the flour, sugar and salt with your fingertips until it looks like coarse breadcrumbs, then work in the egg yolk just until it comes together as a dough. Do not overwork it; a short crust toughens with handling.
2. Press the dough into the base of a 26 cm springform, going about 2 cm up the sides, and chill it for 20 minutes while the oven heats to 160°C.
3. Blind bake the base for 12 minutes, until just set and pale gold. It does not need weights; the sides are short enough not to slump.
4. Beat the quark, sugar and vanilla seeds together until smooth, then beat in the eggs one at a time. Whisk in the cornstarch and finally the oil; the filling should be smooth and pourable, not stiff.
5. Fold in the raspberries gently, keeping them whole, then pour the filling over the warm base.
6. Bake at 160°C for about 55 minutes, until the centre wobbles only slightly in an area no wider than a coffee saucer. Turn the oven off and leave the door ajar for 15 minutes before removing the tin; a sudden temperature change is what cracks the surface.
7. Cool completely, then chill at least 4 hours before slicing. It cuts cleanly cold and softens again at room temperature.

Notes

• Do not open the oven door in the first 40 minutes. A cold draught while the filling is still liquid is the most common cause of a sunken centre.
• The slow cool-down in the switched-off oven is not optional in spirit. A cheesecake pulled straight from a hot oven into room air contracts unevenly and cracks along the surface.
• Well-drained quark matters. A wet quark gives a filling that never fully sets; if using quark from an open tub, tip it into a sieve lined with a tea towel for 30 minutes first.
• It keeps for 4 days in the fridge, covered, and the flavour if anything improves on day two once the raspberries have bled slightly into the filling.

Ingredient substitutions

• Raspberries can be blueberries or pitted sour cherries in the same quantity; frozen fruit works as well as fresh as long as it goes in unthawed, straight from the freezer.
• Quark can be replaced with well-drained Greek yogurt in a pinch, though the texture is denser and slightly tangier than the traditional German result.
• Cornstarch is what keeps this filling from weeping; do not swap it for flour, which gives a pastier texture in a quark filling specifically.
• For a lactose-lighter version, lactose-free quark works identically; the recipe does not depend on the lactose for texture or setting.