You will need 1 x 20cm/8-inch springform cake tin. Put the pieces of white chocolate into a heatproof bowl that will sit on top of a saucepan. Fill the pan with a small amount of water, just enough to come up about 3–4cm / 1½ inches up the sides, and bring to the boil. Sit the bowl of chocolate on top, making sure the base of the bowl doesn’t touch the water. Turn the heat down and let the white chocolate melt very gently, every now and then giving it a careful stir with a silicone spatula. Once there are only a few small lumps of unmelted chocolate left, give it another stir then remove the bowl and sit it somewhere for about 10 minutes, until the chocolate remains liquid but is cooled to room temperature.For the base, break the biscuits into a food processor and blitz until you have almost all crumbs. Add the butter and process again until the mixture starts to clump and cleave to the blade. If doing this by hand, put the biscuits into a bag, crush to crumbs, then melt the butter and stir into the biscuit crumbs until well mixed.Press the biscuit mixture into the springform cake tin, letting some come a little way up the sides. The back of a dessert or serving spoon is the easiest tool for the already easy job here. Stash the tin in the fridge while you get on with the cheesecake filling.Beat the cream cheese in a bowl that will take all the ingredients later – a wooden spoon is fine here – until it is soft. Gently fold in the slightly cooled, melted white chocolate.Softly whip the cream so it is thickened but the peaks don’t hold their shape, then fold it into the white chocolate mixture in two batches. Add the lemon juice and vanilla extract and fold these in, then pour and scrape the pale, almost-moussy mixture into the biscuit-lined tin. Smooth the top, cover the tin with cling film and refrigerate overnight before serving.When you’re ready to eat it, make sure it’s been out of the fridge for 10 minutes before unclipping from the tin and cutting it into slices. Don’t expect to be able to remove the whole cheesecake from the tin’s base unless you are both patient and dexterous. I was once foolhardy enough to try…