Authentic Key Lime Pie 
A recipe from the Sneaky Kitchen

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.