1 prepared graham cracker crust
1 (14 oz.) can sweetened condensed milk
1 (8 oz.) Cool Whip
1/2 to 3/4 c. Key lime juice (does not have to be Key limes)

Combine condensed milk and lime juice thoroughly. Add 1/2 of the Cool Whip and fold in. Pour into prepared graham cracker crust. Spread other half of Cool Whip on top. Refrigerate.