Key lime pie is made of Key lime juice, eggs, condensed milk, and sugar in a pre-baked 
pie shell. The pie is then baked, often with a meringue on its top. Other recipes (with 
slightly different ingredients) call for it to be chilled or frozen, using an unbaked 
Graham cracker crust. This makes it a popular summer dessert. The dish is named after 
the small Key limes (Citrus aurantifolia 'Swingle') that are naturalized throughout the 
Florida Keys. Their ferocious thorns make them less tractable and their thin yellowish 
rind makes them less shippable, but they are both tarter and more aromatic than the 
common Persian limes seen year-round in most U.S. grocery stores.

Proper Key lime pie is made with canned sweetened condensed milk, since fresh milk was 
not a common commodity in the Florida Keys before modern refrigerated distribution 
methods.

Key lime juice, unlike regular lime juice, is a pale yellow. As such, Key lime pies are 
also pale yellow.[1] Green Key lime pies, such as the one in the opening scene of 
Natural Born Killers, are not authentic,[2] and the green color is due to added food 
coloring. Many "Key lime" pies are made with standard Persian limes since they tend to 
be larger and yield more juice, thus making them easier to work with.

During mixing, a reaction between the condensed milk and the acidic lime juice occurs 
which causes the filling to thicken on its own without requiring baking. Many early 
recipes for key lime pie did not instruct the cook to bake the pie, relying on this 
chemical reaction to produce the proper consistency of the filling. Today, in the 
interest of safety due to consumption of raw eggs, pies of this nature are usually 
baked for a short time. The baking also thickens the texture more than the reaction 
alone.

Ingredients

    * 1 prepared 9-inch (9 oz.) Graham cracker crust
    * 1 can (14 oz.) sweetened condensed milk
    * ½ cup fresh Key lime juice
    * 1 tsp. grated lime zest
    * 2 cups whipped topping or whipped cream
    * lime slices (optional)

Equipment and supplies

small mixing bowl, spatula, stand mixer.

Procedure

   1. Begin by beating the sweetened condensed milk and lime juice in a small mixer 
bowl.
   2. Pour the milk and lime juice mixture into the Graham cracker crust.
   3. Spread with whipped topping.
   4. Refrigerate for 2 hours or until it is set.
   5. Lime slices can be used for garnish.

Notes, tips, and variations

    * There are several variations that require cooking.
    * There are several variations that call for raw egg yolks.
    * If eggs are used, the yolks go in the pie and the whites can be used to make a 
meringue.
    * Raw eggs can be hazardous to your health.