Prepare the crust: Place the digestive biscuits into a large zip-top bag and seal it, squeezing out the air. Use a rolling pin to crush them until you have fine crumbs with no large chunks — you should hear a soft, sandy sound as you roll. Tip the crumbs into a medium bowl, add the 2 tablespoons of caster sugar, and pour over the melted butter. Stir with a fork until every crumb is coated and the mixture looks like wet sand and clumps together when squeezed in your fist.

Press the crust: Tip the buttery crumbs into a 20cm (8-inch) springform tin. Use the bottom of a flat glass or a measuring cup to press the crumbs firmly and evenly into the base — press hard enough that you feel resistance, creating a compact, solid layer. Place the tin in the fridge to chill while you prepare the filling.

Bloom the gelatine (optional): If using gelatine for a firmer set, sprinkle the powder over the 3 tablespoons of cold water in a small bowl. Let it sit for 5–10 minutes until it becomes a spongy, solid mass — it should look like a wobbly, translucent jelly. Set aside.

Make the lemon cream cheese base: In a large mixing bowl, beat the softened cream cheese with an electric hand mixer on medium speed until it’s completely smooth and glossy — about 2 minutes, scraping down the sides halfway through. Add the 150g of caster sugar, the lemon zest, vanilla extract, and the pinch of salt. Beat again until the sugar is dissolved and the mixture feels silky and slightly gritty only from the zest.

Add the lemon juice: With the mixer on low speed, slowly pour in the fresh lemon juice. The mixture will look slightly curdled or separated at this point — do not panic, this is completely normal. It will come back together once the cream is added. If using gelatine, now is the time to gently warm the bloomed gelatine in the microwave for 10 seconds until it becomes a liquid, then pour it in with the lemon juice and mix well.

Whip the cream: In a separate clean bowl, pour in the double cream and beat on medium-high speed until it holds soft peaks — when you lift the beaters, the cream should droop slightly but hold its shape. You should hear the beaters change sound from a slosh to a gentle thwack as the cream thickens.

Fold everything together: Add one-third of the whipped cream to the cream cheese mixture and fold gently with a spatula using a figure-eight motion. This lightens the mixture. Once combined, add the remaining cream and fold until no white streaks remain — the mixture should look uniform, pale yellow, and feel airy and mousse-like when you lift the spatula.

Assemble and chill: Pour the filling into the chilled crust and spread it evenly with the spatula, smoothing the top. Give the tin a gentle tap on the countertop to release any trapped air bubbles. Cover loosely with cling film and refrigerate for at least 4 hours, but ideally overnight — the filling should feel firm to the touch and the surface should look set and slightly shiny when ready.