Pre-made graham cracker crust
Cool Whip (or other whipped topping)
3 egg yolks
3/4 c. lime juice
1 can sweetened condensed milk
Few drops green food coloring

Beat together egg yolks and condensed milk. Add lime juice and food coloring, stirring well. Pour into pre-made graham cracker crust. Refrigerate 2 hours. Serve with whipped topping.