Beat the egg whites until frothy. Add cream of tartar and gradually beat in 1 cup (250 ml) of the sugar until stiff peaks form. Spread the mixture in a greased 9-inch (23 cm) pie pan and bake in a preheated 275F (135C) oven for 20 minutes. Increase the temperature to 300F (150C) and bake an additional 40 minutes. Remove the meringue from the pie pan immediately and cool on a wire rack. Meanwhile, beat the egg yolks and remaining sugar until thick and lemon-colored. Stir in the lemon juice and rind and cook in a saucepan set over a pot of simmering water until
Serves 6 to 8.