Process the biscuits until they are like crumbs, then add the butter and pulse again. Line the bottom of the Springform tin, pressing the biscuits in with your hands or the back of a spoon. Put the tin in the fridge to set, and preheat the oven to 180ºC/gas mark 4.
Beat the cream cheese gently until it's smooth, then add the sugar. Beat in the eggs and egg yolks, then finally the vanilla and lemon juice. Put the kettle on.
Line the outside of the chilled tin with strong foil so that it covers the bottom and sides in one large piece, and then do the same again and put it into a roasting dish. This will protect the cheesecake from the water as it is cooked in its water bath.
Pour the cream-cheese filling into the chilled biscuit base, and then pour hot water from the recently boiled kettle into the roasting tin around the cheesecake. It should come about halfway up; don't overfill as it will be difficult to lift up the tin. Put it into the oven and cook for 50 minutes. It should feel set, but not rigidly so: you just need to feel confident that when you pour the sour cream over, it will sit on the surface and not sink in. Whisk together the sour cream, sugar and vanilla for the topping and pour over the cheesecake. Put it back in the oven for a further 10 minutes.
Take the roasting tin out of the oven, then gingerly remove the Springform, unwrap it and stand it on a rack to cool. When it's cooled down completely, put it in the fridge, removing it 20 minutes before eating to take the chill off. Unmould and when you cut into it, plunge a knife in hot water first.
Additional information - for vegetarians check that the cream cheese is a brand that does not contain rennet.