Baked Blueberry Cheesecake with Glossy Blueberry Topping

Method

1. Preheat the oven to 325°F/320°F. Position a rack in the middle. Prepare a 20 cm springform pan: turn the base upside down, butter it lightly, press a square of parchment paper onto it, then clip the sides on. Butter and line the sides with parchment as well.
2. For the crust: break the biscuits into a food processor and blitz to fine crumbs. Add the melted butter and pulse until the mixture looks like wet sand. Transfer to the prepared pan. Use a spatula to spread the crumbs over the base and up the sides, then press firmly with a flat-bottomed object (like a measuring cup) to form an even crust almost to the top.
3. For the filling: in a stand mixer with paddle attachment (or with a hand mixer), beat the cream cheese on speed 4 just until smooth—no more than 20 seconds. Add the flour and beat for 5 seconds on speed 4. Then add the vanilla, sour cream, sugar, and lemon zest; beat until just combined (about 10 seconds on speed 4).
4. Add the eggs one at a time, beating for 5 seconds on speed 4 after each. After the last egg, beat just until the batter is smooth—stop immediately. Gently fold in the 250 g of blueberries with a rubber spatula. Pour the filling into the prepared crust.
5. Bake for 70 minutes. The top should be slightly puffed, very light golden, not cracked, and nearly flat. It should jiggle slightly when you gently shake the pan. Turn off the oven, open the door about 20 cm, and let the cheesecake cool inside for about 2 hours. Then refrigerate in the pan for at least 4 hours (or overnight).
6. To release: remove the springform sides. Use the parchment overhang to slide the cheesecake off the base, then slide it off the paper. Place on a serving plate.
7. For the blueberry sauce: in a saucepan, combine 125 g (1 cup) of the blueberries, the vanilla, sugar, and lemon juice. Stir and bring to a simmer over medium heat. Cook for 7 minutes, until the blueberries break down. Mix the cornflour with the 2 tbsp water and stir into the saucepan; it will thicken quickly.
8. Stir in the remaining 250 g of blueberries. The sauce should be syrupy. Remove from heat and let cool. It will thicken further as it cools. Once cool, stir and adjust consistency with a few drops of water if needed—it should ooze, not be runny.
9. Spoon the sauce over the cheesecake to cover it completely. You will have about 1/2 cup extra for touch-ups. Refrigerate for at least 2 hours before slicing and serving.