Ingredients
For the crust
85g butter, plus extra for tin
140g digestive biscuits, made into fine crumbs (add 2 extra biscuits if you like a thicker base)
1 tbsp sugar, granulated or golden caster
For the cheesecake filling
900g Philadelphia cheese, or other full-fat soft cheese
250g golden caster sugar
3 tbsp plain flour
1½ tsp vanilla extract
finely grated zest of 1 lemon (about 2 tsp)
1½ tsp lemon juice
3 large eggs, plus 1 yolk
284ml carton soured cream
For the soured cream topping
142ml carton soured cream
1 tbsp golden caster sugar
2 tsp lemon juice
Method
Position an oven shelf in the middle of the oven. Heat the oven to 180C/ 160C fan/ gas 4.
Line the base of a 23cm springform cake tin by putting a square piece of parchment paper or foil on top of the tin base and then clipping the side on so the paper or foil is trapped and any excess sticks out of the bottom.
For the crust, melt 85g butter in a medium pan. Stir in 140g digestive biscuit crumbs and 1 tbsp golden caster or granulated sugar so the mixture is evenly moistened.
Press the mixture into the bottom of the pan and bake for 10 minutes. Cool on a wire rack while preparing the filling.
For the filling, increase the oven temperature to fan 220C/ 200C fan/ gas 7. In a table top mixer fitted with the paddle attachment, beat 900g full-fat soft cheese at medium-low speed until creamy, about 2 minutes.
With the mixer on low, gradually add 250g golden caster sugar, then 3 tbsp plain flour and a pinch of salt, scraping down the sides of the bowl and the paddle twice.
Swap the paddle attachment for the whisk. Continue by adding 1½ tsp vanilla extract, 2 tsp lemon zest and 1½ tsp lemon juice. Whisk in 3 large eggs and 1 yolk, one at a time, scraping the bowl and whisk at least twice.
Stir a 284ml carton of soured cream until smooth, then measure 200ml (just over ¾ of the carton). Continue on low speed as you add the measured soured cream (reserve the rest). Whisk to blend, but don't over-beat. The batter should be smooth, light and somewhat airy.
Brush the sides of the springform tin with melted butter and put on a baking sheet. Pour in the filling - if there are any lumps, sink them using a knife - the top should be as smooth as possible. Bake for 10 minutes.
Reduce oven temperature to 110C/ 90C fan/ gas ¼ and bake for 45 minutes more. If you gently shake the tin, the filling should have a slight wobble.
Turn off the oven and open the oven door for a cheesecake that's creamy in the centre, or leave it closed if you prefer a drier texture. Let cool in the oven for 2 hours. The cheesecake may get a slight crack on top as it cools.
Combine the reserved soured cream with a 142ml carton soured cream, 1 tbsp golden caster sugar and 2 tsp lemon juice for the topping. Spread over the cheesecake right to the edges. Cover loosely with foil and refrigerate for at least 8 hours or overnight.
Run a round-bladed knife around the sides of the tin to loosen any stuck edges. Unlock the side, slide the cheesecake off the bottom of the tin onto a plate, then slide the parchment paper out from underneath.