Prep the pan and oven: Heat the oven to 325°F (163°C). Wrap the outside of a 9-inch springform pan with a few layers of foil to keep water out. Lightly grease the inside.
Make the crust: Combine graham crumbs, sugar, salt, and melted butter. Press firmly into the bottom and slightly up the sides of the pan. Bake for 8–10 minutes until set. Cool slightly.
Mix the filling base: Beat cream cheese and sugar on medium speed until smooth, about 2 minutes. Scrape the bowl. Add sour cream, lemon zest, lemon juice, vanilla, and salt. Mix until combined and creamy.
Add the eggs: Beat in eggs one at a time on low speed, just until blended. Do not overmix; too much air can cause cracks.
Set up the water bath: Pour the filling over the crust. Place the pan in a roasting pan. Pour hot water into the roasting pan to reach halfway up the springform sides.
Bake the cheesecake: Bake 55–70 minutes. The edges should be set, with a slight wobble in the center. Internal temperature at the center should be around 150–155°F if using a thermometer.
Cool gently: Turn the oven off, crack the door, and let the cheesecake sit for 1 hour. Remove from the water bath, unwrap foil, and cool to room temperature. Then chill at least 6 hours, preferably overnight.
Make the lemon curd: In a heatproof bowl, whisk yolks, sugar, lemon juice, zest, and salt. Set over a pot of barely simmering water and whisk until thickened, 8–12 minutes, or until it coats the back of a spoon. Whisk in butter until glossy. Strain for a silky finish. Cool to room temp, then chill.
Top with curd: Once the cheesecake is fully chilled and set, spread an even layer of lemon curd over the top, leaving a small border if you like. Chill 30 minutes to firm.
Whip the meringue: Beat egg whites with cream of tartar and salt to soft peaks. Gradually add sugar, a tablespoon at a time, beating to stiff, glossy peaks. Beat in vanilla.
Finish and toast: Spoon or pipe meringue over the chilled curd, creating swoops and peaks. Toast with a kitchen torch until golden, or place under a broiler for 1–2 minutes, watching constantly. Chill 15–30 minutes before slicing.
Slice cleanly: Warm a sharp knife under hot water, wipe dry, and cut. Wipe the blade between slices for neat edges.