Preheat oven to 350°F (180°C). Mix graham cracker crumbs, melted butter, and sugar. Press into a springform pan and bake for 10 minutes. Let cool.,Beat cream cheese and sugar until smooth. Add eggs one at a time. Mix in lemon juice, zest, vanilla, and sour cream. Pour over crust and bake 50–60 minutes. Cool completely, then chill for at least 3 hours.,Whisk lemon juice, zest, sugar, egg yolks, and cornstarch in a saucepan over medium heat until thick. Cool slightly, then spread over cheesecake.,Whip egg whites with cream of tartar until soft peaks form. Gradually add sugar and beat to stiff peaks. Spread or pipe over lemon layer. Brown under broiler or with a torch.,Chill before serving.