Beat egg whites (at room temperature) until foamy; add cream of tartar, beating slightly. Gradually add 1 cup sugar, beating well after each addition; continue beating egg mixture until stiff and glossy. Do not under beat mixture.
Spoon meringue into a well greased 9-inch pie plate. Use a spoon to shape meringue into a pie shell, swirling sides high. Bake at 275° for 50 minutes. Set aside to cool.
Beat egg yolks until thick and lemon colored. Gradually add remaining 1/2 cup sugar, lemon rind and juice, and salt. Cook in top of a double boiler, stirring constantly, until smooth and thickened. Cool mixture.
Fold 1 cup whipped cream into lemon mixture; spoon into meringue shell, and spread evenly. Cover and refrigerate at least 12 hours. Top with additional whipped cream.