Prepare the crust. Place the digestive biscuits in a sealed bag and crush them with a rolling pin until they resemble fine, golden sand. You want a uniform texture — no large chunks. Tip the crumbs into a bowl, pour over the melted butter, and stir until every grain is coated and the mixture smells wonderfully toasty. Press this firmly into the base of a 23cm springform tin lined with parchment paper. Use the flat bottom of a glass to really compact it down. Bake at 160°C for 10 minutes — it should look a shade darker and smell nutty. Set aside to cool.

Begin the filling. In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese on low speed for a minute until it's soft and smooth. You're looking for a texture like thick, spreadable butter — no lumps at all. Scrape down the bowl and the beater well.

Add the sugar and dry ingredients. Add the caster sugar, flour, vanilla, lemon zest, and salt. Mix on low speed until everything is just combined. The mixture will look glossy and slightly grainy. Do not overmix — we don't want to incorporate too much air.

Add the eggs one by one. Crack the first egg into a small bowl to check for shell, then add it to the mixer on low speed. Wait until you no longer see yellow streaks — about 15 seconds — before adding the next. The batter will become looser and more fluid with each egg. Add the extra yolk last. The mixture should now be pale, smooth, and smell distinctly of vanilla.

Fold in the cream. Remove the bowl from the mixer. Pour in the double cream and use a large rubber spatula to fold it in gently. Use a slow, sweeping motion from the bottom up. The batter will become lighter, silkier, and a shade paler. Stop as soon as the cream disappears — no further.

Prepare the water bath. Wrap the outside of your springform tin with two layers of strong foil, bringing it up the sides. Place the tin in a large, deep roasting tray. Pour the cheesecake batter into the prepared crust, smoothing the top with a spatula. The surface should be level and glossy.

Bake low and slow. Place the roasting tray on the middle oven rack. Carefully pour hot (not boiling) water into the roasting tray until it reaches halfway up the sides of the springform tin. Close the oven door gently. Bake at 160°C for 50-60 minutes. The edges will look puffed and set, but the centre should have a distinct wobble — like a firm jelly. The top should be a pale, matte gold, and you'll smell the sweet, buttery aroma filling your kitchen.

Cool gradually. Turn the oven off and crack the door open with a wooden spoon. Leave the cheesecake in the warm oven for one hour. This gentle cooling prevents the surface from cracking. After an hour, remove the tin from the water bath, take off the foil, and place it on a wire cooling rack until it reaches room temperature. The top will settle and become flat and even.

Chill overnight. Once completely cool, cover the tin tightly with cling film and refrigerate for at least 6 hours, but preferably overnight. This is the crucial step where the cheesecake sets into its signature dense, sliceable texture. The aroma will be fainter now, but the promise of that first bite is worth the wait.