For filling, in a large bowl, stir together egg yolks and sweetened condensed milk. Stir in lime peel. Gradually stir in lime juice and, if you like, food coloring (mixture will thicken). Pour into Baked Pastry Shell.
Bake in a 350 degree F oven for 30 minutes. Remove from oven; cool completely on wire rack.
To serve, pipe or dollop the whipped cream or whipped topping on top of pie, if you like. Makes 10 servings.
Prepare as above, except substitute 1 to 2 tablespoons finely shredded orange peel for the lime peel and 2/3 cup lemon juice for the lime juice.
Stir together flour and salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon of the water over part of the mixture; gently toss with a fork. Push moistened dough to the side of the bowl. Repeat moistening dough, using 1 tablespoon of the water at a time, until all the dough is moistened. Form dough into a ball. On a lightly floured surface, use your hands to slightly flatten dough. Roll dough from center to edge into a circle about 12 inches in diameter. To transfer pastry, wrap it around the rolling pin. Unroll pastry into a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch pastry. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry. Crimp edge as desired. Generously prick bottom and side of pastry in pie plate with a fork. Prick all around where bottom and side meet. Line pastry with a double thickness of foil. Bake in a 450 degree F oven for 8 minutes. Remove foil. Bake 5 to 6 minutes more or until golden. Cool on a wire rack.