The Tragical Comedy, or Comical Tragedy, of Key Lime Pie: a juggling performance in four acts
ACT I: CRUST
2 sticks butter (or use leaf lard or vegetable shortening)
2 1/2 cups all-purpose flour
1 Tbsp sugar
1 Tbsp salt
About 1/3 cup water
1 egg yolk
1 pinch salt
This is the standard Joy of Cooking flaky pastry recipe. Cut the butter into pieces and rub it into the flour, sugar, and salt until it reaches a texture like coarse crumbs, with a few lumps of butter here and there. Pour in the water. Mix just until it congeals into a big rough ball. Chill in the refrigerator for 1/2 hour or more.
Preheat the oven to 400 degrees. Take the dough out of the refrigerator and divide it into two balls. Flour a rolling pin and a board and roll out the dough. Place it into two pie pans and trim off the overhanging edges. (If you're patient, put them back into the fridge for another hour or so to let them relax so they won't shrink in the oven. I am not patient.) Put a big square of tinfoil over each pan. (The edges should cover the entire pie crust, to keep it from browning too much at first.) Put raw beans, rice, or pie weights into the foil to weigh down the pie and keep the crust from bubbling and puffing. I have a Ziplok bag labeled "PIE BEANS" in my cabinet. I imagine it is a fairly cryptic artifact to come across, unless you bake pie crusts from scratch.
Begin Act II. Bake the crusts for 20 minutes.
Remove the crusts from the oven, take the foil and pie weights out of them, and prick them all over with a fork. Place them back into the oven for about 10 or 15 minutes to let them brown.
Take the crusts back out. Whisk together the egg yolk and salt. Brush the crusts with the egg yolk to waterproof them, and put them back in the oven for a few more minutes to let the egg yolk cook.
ACT II: FILLING
1/2 cup lime juice
3-4 tsp lime zest
1 (14 or 15-ounce) can of sweetened condensed milk, of any fat content
4 egg yolks
Preheat the oven to 325 degrees. Mix everything together. Divide the filling between the two crusts. Go to Act III; prepare the cornstarch paste. Place the pies in the oven and bake for 5-7 minutes, until the filling is just thick enough to support the meringue. While the filling is baking, go immediately to Act IV.
ACT III: MERINGUE
1 Tbsp sugar
1 Tbsp cornstarch
1/3 cup water
4 egg whites
1/4 tsp cream of tartar
1/2 tsp vanilla extract
1/2 cup sugar
Mix the cornstarch and 1 Tbsp sugar together in a small saucepan. Add the water very gradually (or the cornstarch will become lumpy) and heat the mixture to a boil, stirring vigorously. Let the mixture boil for about 15 seconds, stirring the whole time, then remove from the heat and cover. You should have a translucent paste.
Place the egg whites in a clean, greaseless, yolk-free bowl. Beat until foamy. Add the vanilla and cream of tartar, then the 1/2 cup sugar, little by little, and then whip at high speed until it forms stiff peaks. It should not look dry yet.
Add the cornstarch paste a little bit at a time, beating at low speed. When all the cornstarch has been mixed in, beat at medium speed for 15 seconds.
ACT IV: IT ALL COMES TOGETHER
Once the meringue has been prepared, it won't last long.
The crust must be filled while it's hot, or it will get soggy.
The meringue must go onto the filling while it's hot, or it won't cook properly--it will get soft and weep, since the bottom surface won't cook as quickly as the top unless the hot lime filling is cooking it from underneath at the same time.
So: as soon as the pies have been filled, the meringue has been whipped to peaks, and the filling has been baked just enough to set it, remove the pies from the oven. Dab a band of meringue around the edges, making sure it touches the crust all the way around; if it doesn't, it will pull back at that point. Fill in the center with more meringue. Smooth it out. Bake for another 20 minutes, and then remove the pies and let them cool.