Preheat the oven to 180°C (gas mark 6) for 15 minutes. Butter the sides of the tin -
Cut out two lengths of greaseproof paper 8cm wide and line the sides of the tin - it will stick to the buttered surfaces - (the paper will come over the top by 3cm)
Reduce the biscuits to a powder (put them in a plastic bag and crush them with a rolling pin).
Melt the butter.
Mix the biscuits and melted butter with a wooden spatula and then with your hands to make a ball of coarse dough. Place it in the springform tin - spread out evenly and use the palm of your hand to press it well into the tin.
Place it in the oven at 180° (gas mark 6) for 15 minutes and then remove it.
Increase the oven temperature to 200° (gas mark 7)
Whisk the Philadelphia and then add the following, in order, whisking a little after each - the sugar, flour, eggs and two egg yolks one by one, the vanilla extract, lemon and crème fraîche.
Pour the cream over the base and cook for 15 minutes at 200° (gas mark 7). Then reduce the oven to 100°C and cook for a further 60 minutes.
Turn off the oven and leave the cheesecake inside it for one hour with the door ajar.
Allow the cheesecake to completely cool on the outside and then remove it from the tin and place it in the refrigerator for 12 hours.