Prepare the Crust: Preheat oven to 325°F (160°C). Mix graham cracker crumbs, sugar, and melted butter until evenly coated. Press firmly into the bottom of a 9-inch springform pan. Bake for 8–10 minutes. Let cool.
Make the Cheesecake Filling: Beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well after each. Stir in sour cream, flour, lemon juice, lemon zest, and vanilla. Pour over the cooled crust. Bake for 50–60 minutes, until the center is set but slightly jiggly. Cool completely, then chill for at least 4 hours or overnight.
Prepare the Lemon Curd: In a saucepan over medium heat, whisk lemon juice, zest, sugar, and egg yolks. Cook until thickened, about 5–7 minutes, stirring constantly. Remove from heat and stir in butter until smooth. Let cool, then spread over the chilled cheesecake.
Make the Meringue: In a clean bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating until stiff, glossy peaks form. Mix in vanilla.
Assemble & Toast: Spread meringue over the lemon curd layer. Use a kitchen torch or broil briefly in the oven to lightly toast the peaks. Chill until ready to serve.
Serving and Storage Tips
