Prepare the Meringue Crust: Preheat oven to 325°F (163°C). Beat egg whites with cream of tartar until foamy, gradually add ½ cup sugar until stiff peaks form. Spread into a greased 9-inch pie plate and bake for 25 minutes. Cool completely.
Make the Lemon Filling: Mix remaining sugar with cornstarch, water, lemon juice, and zest in a saucepan. Cook until thickened, then cool slightly before beating in egg yolks. Return to heat and thicken further. Cool completely.
Assemble the Pie: Whip the cream to peaks, fold into lemon filling, and spoon into crust. Chill for at least 4 hours.