Beat egg yolks until thick and lemon-colored. Gradually beat in sugar. Stir in lemon juice and peel. Cook over simmering water, stirring constantly, until mixture is thick, about 5 to 8 minutes. Mixture should be thick enough to mound slightly when dropped from spoon. Cool.
Spread cool lemon mixture into Meringue Pie Shell. Top with whipped cream. Chill 12 hours or overnight.