Preheat oven to 350°F (175°C). Mix graham cracker crumbs, melted butter, and sugar, then press into a springform pan and bake for 8–10 minutes. Let cool.
Beat cream cheese until smooth, then add sugar, eggs, sour cream, and vanilla extract. Mix until creamy.
Pour filling over crust and bake for 40–45 minutes until center is just set. Cool completely, then refrigerate.
In a saucepan, whisk lemon juice, zest, sugar, egg yolks, and cornstarch. Cook until thickened, then cool slightly and spread over cheesecake.
Beat egg whites and cream of tartar until soft peaks form. Gradually add sugar and beat until stiff peaks form.
Spread meringue over the lemon layer, sealing edges.
Lightly toast the meringue using a torch or broiler.