Double Lemon Cheesecake Bars

Crust:
1 1/2 c. graham cracker crumbs
1/2 c. butter, melted
1/2 c. sugar
Filling:
4 eggs, divided
4 pkgs. (8 oz each) cream cheese, softened
1 3/4 c. sugar, divided
3 T. flour
1 T. lemon zest
1/3 c. lemon juice (from 2 lemons), divided
1/2 t. vanilla
2 T. cornstarch
1/2 c. water

Heat oven to 350. Combine all crust ingredients and press into the bottom of a 9x13 dish that has been sprayed. Bake 10 minutes until toasted but not burned. Reduce oven to 325. Beat cream cheese, 1 c. sugar, flour, lemon zest, 2 T. lemon juice,and vanilla. Add 3 whole eggs, 1 at a time, and 1 egg white. Mixing on low just until blended. Reserve egg yolk until ready to use. Pour over crust. Bake 40 minutes until center is almost set. Cool 1 hour. Refrigerate 4 hours. Combine cornstarch & 3/4 c. sugar in saucepan. Gradually stir in water and remaining lemon juice until blended. Bring just to a boil, stirring constantly, until clear and thickened. Lightly beat egg yolk with fork, until blended, stir in 2 T. of hot cornstarch mixture. Return this mixture to the cornstarch mixture in saucepan and stir until blended. Cook 1 minute until thickened, stirring constantly. Cool slightly. Spoon over cheesecake. Refrigerate 1 hour until firm before serving.