1: Preheat the oven to 180°C / Fan 160°C / Gas 4.
2: Lightly grease the base and sides of. A23cm round springform cake tin with butter and line with non-stick baking parchment. Butter the parchments.
3: To make the base, put the biscuits into a food processor and whiz to crumbs. Alternatively, place them in a self-sealing plastic bag and bash with a rolling pin until finely crushed. Tip the crumbs into a large bowl and stir in the sugar, add the melted butter and mix to combine.
4: Tip the crumb mixture into the prepared cake tin, spread evenly and press down firmly with the back of a spoon so the base is nice and compact. Bake for 10-15 minutes. Remove from the oven and leave to cool completely in the tin.
5: Meanwhile, prepare the filling. Using either a freestanding mixer fitted with the whisk attachment or an electric hand mixer and bowl, beat the cream cheese, crème fraiche and sugar together on a medium speed for a couple of minutes until the mixture is very smooth and creamy.
6: Sift the flour and salt over the mixture and mix again briefly, just to combine. Add the vanilla seeds, lime juice and zest, and whisk slowly, until evenly blended. Now incorporate the egg yolks one at a time, beating briefly after each addition and scraping the bowl down as necessary with a spatula. Do not overbeat – you want the filling to be smooth, light and aerated.
7: Pour the filling on top of the biscuit base, gently levelling out the surface with a spoon or a palette knife. Give the tin a gentle tap on a flat surface to ensure there are no air pockets in the mixture and stand the tin on a baking sheet.
8: Bake at 180°C/160°C/Gas 4 for 10 minutes, then turn the oven own to 140°C/ Fan 120°C/ Gas 1 and bake for a further 1 hour and 10 minutes. The filling should be set but have a slight wobble in the centre when you gently shake the tin. Do not overcook as it will firm up considerably as it cools.
9: Turn off the oven and prop the oven door open slightly, leave the cheesecake inside to ‘rest’ for around 15-20 minutes, then remove from the oven and leave to stand at room temperature for at least 3 hours. It’s now ready to serve but can be chilled if you’re not eating it straight.
10: To unmould the cheesecake, run a knife around the edge of the tin, removing he parchment and transfer the cheesecake to a place cut into wedges and serve just as it is, or with fruit.