From Heather Dewar
This is another PAB (and Byrne-McKinney) favorite. Straight from the source, unedited, with FYI’s from a native Floridian (there actually are some!).
When shopping for key limes, try to find ones that are starting to turn yellow. Ripe key limes are yellow, not green. Green limes don’t have enough pectin for the pie to set well. Ripe ones are hard to find up north, so try to shop for them several days in advance and let them ripen in a paper bag. If you can’t find them, Nellie & Joe’s Key West lime juice in a yellow plastic bottle makes a perfectly fine substitute. Seriously. No one will know. Just make sure you don’t get Nellie & Joe’s lemon juice by mistake. That, they’ll know.
For a deep dish pie, double the filling recipe. You may have a quarter-cup or so more filling than you need. If so, just bake it in a small soufflé cup or something similar when you bake the pie. A lagniappe for the cook!
Make a standard graham cracker crust, but substitute ginger snaps for the graham crackers. Chill the crust for a few minutes while you make the pie filling.
Preheat oven to 350.
1 can Eagle brand sweetened condensed milk
3 large or extra-large egg yolks
1/3-1/2 cup key lime juice (from about 10 limes)
Beat together the condensed milk and egg yolks. Gradually add at least 1/3 c and up to 1/2 cup of lime juice. The mixture should start to set up as you’re whisking it, the way an instant pudding would. (The goal is to add as much juice as you can, for maximum tartness without making key lime soup. Maxing out the pectin in the fruit is key! Though key lime soup is not bad. The amount will vary with the ripeness of your limes.) When the rate of setting up slows down noticeably, stop adding more lime juice.
Pour batter into ginger snap crust pie shell. Protect the edges of the crust from burning by crimping aluminum foil around the rim of the pie plate to just cover the crust.
Bake at 350 15 minutes. Do not over bake or the texture will be chalky.
Serve cool or at room temp with whipped cream - never meringue!