Line a 20cm (8 inch) spring-form cake tin with baking parchment.
Process the biscuits in a food processor until they are like crumbs (or break them up by hand by placing in a plastic bag, sealed and then crushed with a rolling pin.
Pour the crushed biscuits into a bowl and pour over the melted butter. Mix together well until combined.
Press the biscuit base into the cake tin and press down well with your hands or the back of a spoon.
Put the tin in the fridge to set (about 30 minutes).
Preheat the oven to 180ºC/gas mark 4.
Beat the cream cheese gently until it's smooth.
Add the sugar and mix well.
Beat in the eggs and egg yolks, then finally the vanilla and lemon juice.
Don't over mix but make sure everything is well incorporated - it should be like a nice thick runny batter.
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.
Pour the 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 (mine took about 60 minutes) 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 and remove cake tin (carefully) from the water bath and foil.
Leave the cheesecake to go cold (still in the cake tin) for at least 2 hours.
Remove the Springform and then place in the fridge (still with cake tin bottom in place) overnight.
In the morning place the cake in the freezer for about one hour (this will help you remove the cake tin base in one piece).
With a knife that has been dipped in boiling water and then wiped, carefully start separating the cheesecake from the cake tin base.
Once base is removed place on cake stand and return to fridge until your ready to serve.
Remove from fridge approx 20 minutes before serving.