Preheat the oven to 250 degrees F ( 120 degrees C).

Beat egg whites until stiff in a clean mixing bowl. Add cream of tartar; gradually add 1 cup sugar, beating until glossy.

Transfer meringue into a well-greased 10-inch pie plate. Spread over bottom and sides of the plate, building up sides 1/2 inch above the edge of the plate.

Bake in the preheated oven for 1 1/2 hours. Turn off the oven; leave meringue inside to cool slowly.

Combine egg yolks, 1/2 cup sugar, 2 teaspoons zest, and lemon juice in a double boiler. Cook, stirring constantly, over medium-low heat until thick.

Pour into a bowl and cool thoroughly.

Whip cold heavy cream in a mixing bowl until stiff. Place 1/2 of the whipped cream in cooled meringue shell. Cover with a layer of lemon filling and top with remaining whipped cream. (This top layer can be piped with a decorative star tip). Garnish with remaining lemon zest. Refrigerate until serving.