Make the biscuit base. Preheat your oven to 160°C (140°C fan). Line the base of a 23cm springform tin with a circle of parchment paper and grease the sides with butter. Crush the biscuits into fine crumbs — I use a sealed food bag and a rolling pin, listening for that satisfying crunch as they break down. Stir in the melted butter and the 1 tablespoon of sugar until the mixture looks like damp sand. Press this firmly into the base of the tin using the flat bottom of a glass. You want an even layer, compact enough that no crumbs shift when you tilt the tin. Bake for 10 minutes, then set aside to cool. The kitchen will smell toasty and buttery.

Prepare the water bath. While the base cools, wrap the outside of your springform tin with two layers of strong foil, bringing it up the sides to prevent any water seeping in. Place the tin inside a larger roasting tray. Boil a kettle of water — you'll need this later.

Make the cheesecake filling. In a large bowl, beat the cream cheese with an electric mixer on medium speed until it's completely smooth and fluffy — about 3 minutes. You'll see it soften and lighten in colour. Add the 200g of sugar and the flour, beating until combined. Scrape down the sides of the bowl well. Add the lemon zest, 4 tablespoons of lemon juice, and the vanilla extract, then beat again. The mixture will smell intensely fresh and citrusy at this point. Add the eggs one at a time, beating on low speed after each addition until just incorporated — overbeating at this stage can cause cracks later. Finally, fold in the soured cream by hand with a spatula until the batter is pale, thick, and silky smooth with no streaks. Pour the filling over the cooled biscuit base and gently smooth the top.

Bake in the water bath. Place the roasting tray with the cheesecake tin into the oven. Carefully pour the boiling water into the roasting tray until it reaches about halfway up the sides of the springform tin. Close the oven door gently. Bake for 50–55 minutes. The cheesecake is ready when the edges look set and slightly puffed, but the centre still wobbles like a firm jelly when you gently shake the tin. The surface should be a pale, matt gold. Turn the oven off and leave the cheesecake inside with the door slightly ajar for 1 hour — this gentle cooling helps prevent cracking.

Cool completely. Remove the cheesecake from the water bath, peel off the foil, and transfer to a wire cooling rack. Run a thin knife around the edge of the tin to loosen the cheesecake, then let it cool to room temperature. The texture will feel firm but tender. Once cool, cover loosely with cling film and refrigerate for at least 4 hours, preferably overnight. The wait is hard, I know, but the filling sets into a dense, creamy slice that is far superior to any rushed version.

Make the blueberry topping. In a small saucepan, combine the blueberries, 80g of granulated sugar, and 1 tablespoon of lemon juice. Place over a medium heat and stir gently. After a few minutes, you'll hear the berries begin to pop and release their deep purple juices. Let it simmer for about 8 minutes, until the mixture has thickened slightly and the berries have softened but mostly held their shape. Stir in the cornflour slurry and cook for another minute — the topping will become glossy and thick enough to coat the back of a spoon. Remove from the heat and let it cool to room temperature. It will continue to thicken as it cools.

Assemble and serve. Unclasp the springform tin and carefully lift the cheesecake onto a serving plate. Spoon the cooled blueberry topping over the top, spreading it gently to the edges, allowing some to drip down the sides if you like that rustic look. Slice with a sharp, hot knife (dip it in hot water and wipe dry between cuts) for the cleanest pieces. The first slice will reveal a creamy, pale interior against the dark jewel-toned topping — a beautiful reward for your patience.