• Mix the sugar, cornstarch, milk, egg yolks and lemon zest in an 8 cup microwave safe bowl. Whisk till it looks like eggnog. Microwave on high for 2 minutes. Whisk well again. Heat and whisk at one minute intervals until the mixture is thick and smooth.
• Add the butter and stir until blended.
• Let the sauce cool, then add sour cream.
• Smooth the mixture into the baked, cooled pie crust and cover with meringue.

Meringue

• Separate the eggs when they are fridge cold. not one speck of yellow is allowed in the whites. Beat the egg whites and cream of tartar until foamy.
• Beat in the sugar, one tbsp at a time. Add vanilla and continue beating till the whites are stiff and glossy. When you lift the beaters there should be miniature Alps mountain peaks.
• Spread the meringue on the lemon filling. Cover the top crust to crust. Sealing the top keeps the meringue from shrinking and weeping. Who wants a wimpy pie?
• Bake at 400 for 8 or 10 minutes. the meringue peaks will be slightly browned and the valleys tan when it is done.