Key lime pie is an American dessert pie. It is made of lime, egg yolks, and sweetened condensed milk. It may be served with no topping, topped with a meringue topping made from egg whites, or with whipped cream; it may be cooked in a pie crust, graham cracker crust, or no crust. The dish is named after the small Key limes, which are more aromatic than the common Persian limes, and which have yellow, not green, juice. The filling in a Key lime pie is also yellow, largely because of the egg yolks.
The filling is made similarly to a Magic Lemon cream pie, by simply mixing the ingredients without cooking: the proteins of the egg yolks and condensed milk and the acidic lime juice curdle, thickening the mixture without baking. Today, key lime pies are usually baked to pasteurize the eggs and thicken the filling further.