Special equipment: a 10-inch springform pan
Preheat the oven to 160°C.
For the crust: Melt the butter in a covered microwave-safe medium bowl in the microwave. Brush a 10-inch springform pan with some of the butter. Stir together the remaining butter with the biscuit crumbs, sugar and salt in a medium bowl. Press the crumb mixture into the bottom and 1 inch up the side of the pan, taking care to get the crust evenly into the edge. Bake until browned, 15 to 18 minutes. Let cool. Wrap the bottom of the pan and up the side with foil, and put the pan on a baking sheet.
For the filling: Beat the cream cheese and sugar in a large bowl with an electric mixer on medium speed for 1 minute. Add the sour cream, and mix until just combined. Add the heavy cream, and mix until just combined. Beat in the eggs one at time. Beat in the vanilla, lemon juice and lemon zest if using until just combined. (Do not overmix, or the cake will turn into a souffle!)
Pour the filling into the crust. Bake until the cake is slightly golden and barely set in the middle, about 1 hour 20 minutes. Turn off the oven, and leave the cake inside with the door shut for 1 hour. It will continue to set and color slightly in the oven.
Run a thin knife or spatula between the cake and the pan to prevent the cake from cracking as it chills. (Mum's cheesecake usually cracked, since she didn't do this.) Refrigerate overnight before serving.
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