Key Lime Pie originated in Key West, Florida in the 1850's by the local residents referred to as "Conchs". The original version was made before the days of refrigeration. There were no cattle in the area so the only milk available was canned milk originally brought in by ship, later by train. The sweetened condensed milk used in this recipe was developed in 1856. This is why the recipe uses canned milk and not fresh. Also, the traditional key lime pie would not be cooked. The acid from the lime juice would set and thicken the egg yolks.
The original pie was made with a simple pastry crust but the graham cracker version has gained in popularity. As for toppings, recipes dating back to 1949 include version with no topping, whipped cream, and meringue.
If you are using the whipping cream garnish, prepare the cream. Serve with a dollop of whipped cream.
Persian lime compared to two key limes