There is only one real authentic recipe for Key Lime Pie, a long-time staple in Key West, although there's many yummy variations. "Conchs", as Key West residents are known, have made this pie since long before refrigeration. There were no cows in Key West, so canned milk was the only dairy product available, originally brought in by ship, later by Flagler's train, and finally by highway.
Authentic Key Lime pie uses tiny yellow Key limes, which are bursting with juice, have more acid and a stronger lime flavor than large limes. Most Key lime trees have wicked thorns, but thornless ones are available. As for the pie, here's the real thing, and it's yellow like Key limes, never green. It's a very rich pie and a little goes a long way
Authentic Key Lime Pie
1 14-ounce can sweetened condensed milk
3 egg yolks
1/2 cup Key Lime Juice
1 9-inch baked pie shell
Whisk the egg yolks into the condensed milk. Add the lime juice little by little, stirring until mixture starts to thicken. Scrape into the pie shell and let it chill and set up.
Some people make meringue with the remaining whites and dress the top of the pie. Some people prefer it with whipped cream or whipped topping, definitely a later invention.
Be aware that non-pasteurized eggs, served raw as is the case with this pie, could carry dangerous salmonella germs.