Preheat oven to 325°F. Line a springform pan with parchment and grease.
Combine graham crumbs and melted butter. Press into pan. Bake 10 mins.
Beat cream cheese until smooth. Add sugar, sour cream, lemon zest, and juice.
Add eggs one at a time, mixing on low. Pour over crust. Bake in water bath for 60 mins.
Cool in oven with door cracked, then chill overnight.
Cook water, cornstarch, yolks, sugar, lemon juice, and butter until thick. Chill lemon curd.
Top cheesecake with lemon curd.
Whip egg whites and cream of tartar until soft peaks. Add sugar gradually to stiff peaks.
Spread meringue over lemon curd. Toast meringue with a torch or broil briefly.