1 can sweetened condensed milk (14 oz., not evaporated milk)
1/2 c. key lime juice (or lemon juice)
3 eggs, separated
9 inch pie shell, baked and cooled (or 1 (9 inch) graham cracker pie crust)

Chill milk overnight in refrigerator. Place cooled milk in a large mixing bowl and beat at high speed of electric mixer for several minutes. Add lime juice a few drops at a time, using a spatula to scrape mixture from sides of bowl. Mixture will begin to thicken.

Add egg yolks, one at a time, and continue to beat. Beat egg whites (with clean beaters) until stiff and gently fold into mixture. Pour filling into pie shell. Chill several hours in freezer.