FOR MERINGUE: Preheat oven to 300 degrees. Beat egg whites, salt and cream of tartar in a large bowl until frothy. Add sugar, 1 tablespoon at a time. Beat until meringue holds very stiff glossy peaks. Grease bottom and sides of a 9 - inch pie plate. Turn meringue into pie plate; making a slight well in the center. Bake at 300 degrees for 10 minutes, reduce heat to 250 degrees and bake for 50 minutes more.
FOR ORANGE FILLING: Beat egg yolks until thick and lemon - colored. Gradually beat in sugar and salt. Add orange juice; beat until combined. Heat in double boiler over hot water until thickened and mixture reaches 160 degrees. Stir in orange rind. Let cool.
FOR WHIPPED CREAM: Beat heavy cream, confectioner's sugar, and vanilla. Stir 2 tablespoons of whipped cream mixture into orange filling. Spoon orange filling into meringue pie shell. Spread remaining whipped cream on top. Garnish if desired. Refrigerate.