Prepare the Tin and Oven: Preheat your oven to 160°C (140°C fan). Grease and line the base of a 23cm (9-inch) springform cake tin with parchment paper. To prepare for the water bath, wrap the outside of the tin in a double layer of heavy-duty aluminium foil, ensuring it comes right up the sides to prevent any water from seeping in.

Make the Biscuit Base: Place the digestive biscuits in a food processor and blitz until they form fine crumbs. Alternatively, put them in a sealed bag and crush them with a rolling pin. Pour the crumbs into a bowl, add the demerara sugar and melted butter, and mix until everything is well combined and resembles wet sand.

Form the Base: Tip the buttery crumbs into your prepared springform tin. Use the back of a spoon or the base of a glass to press the mixture down firmly and evenly across the bottom and slightly up the sides. Place the tin in the fridge to chill while you make the filling.

Start the Filling: In a large bowl using a stand mixer with the paddle attachment or a hand mixer, beat the room-temperature cream cheese on a low speed for 1-2 minutes until it's smooth and free of lumps. Scrape down the sides and bottom of the bowl.

Combine the Wet Ingredients: Add the caster sugar and plain flour to the cream cheese and beat on low speed until just combined. Add the eggs and egg yolk one at a time, mixing gently after each addition until just incorporated. What works best for me is to keep the mixer speed low throughout this process to avoid whipping too much air into the batter, which can cause cracks.

Finish the Filling: Gently fold in the soured cream, vanilla, lemon zest, and lemon juice with a spatula until the batter is smooth and uniform. Take care not to over-mix.

Assemble and Bake: Pour the filling over your chilled biscuit base and smooth the top. Place the springform tin into a large roasting tray. Carefully pour boiling water into the roasting tray so that it comes about halfway up the sides of the cake tin.

Bake and Cool: Carefully transfer the roasting tray to the preheated oven. Bake for 60 minutes. The cheesecake should be set around the edges but still have a slight wobble in the centre. Turn off the oven, prop the oven door open slightly with a wooden spoon, and leave the cheesecake inside to cool down completely for at least 1-2 hours. This gradual cooling is the ultimate trick for a flawless finish.

Chill Thoroughly: Once completely cool, remove the cheesecake from the water bath and take off the foil. Cover it loosely with cling film and transfer it to the refrigerator to chill for at least 6 hours, but preferably overnight. This step is essential for the cheesecake to set fully, allowing for clean, beautiful slices.