Ingredients

Equipment Needed

• •9-inch pie plate (glass or ceramic)
• •Microplane or fine grater for zesting
• •Citrus juicer or reamer
• •Fine-mesh strainer for seeds
• •Electric mixer or large whisk for cream

Instructions

1. 1

   Prepare the crust

   Position a rack in the center of your oven and preheat to 350°F. Combine graham cracker crumbs, sugar, and salt in a medium bowl. Pour in the melted butter and stir with a fork until every crumb is coated and the mixture resembles damp sand. It should clump when you squeeze a handful.

   For the finest crumbs, pulse whole graham crackers in a food processor. Hand-crushed crumbs in a zip-lock bag work too, but expect a rustier texture.
2. 2

   Press and bake the crust

   Transfer the crumb mixture to a 9-inch pie plate. Using the bottom of a measuring cup or the flat of your palm, press crumbs firmly across the bottom and up the sides, building a compact wall about 1/4-inch thick. The bottom should feel solid when you rap it with your knuckles. Bake until the crust turns golden and fragrant, 10 to 12 minutes. The kitchen will smell like toasted cookies. Set aside to cool while you make the filling.

3. 3

   Zest before juicing

   Using a microplane or the fine holes of a box grater, zest six Key limes before cutting them. You need one tablespoon of zest. Work gently, taking only the thin green layer. The white pith beneath is bitter and will muddy your filling. Set zest aside.

   Key limes have thinner skins than Persian limes. One pass with the microplane is usually enough.
4. 4

   Juice the limes

   Cut your Key limes in half crosswise and juice them through a small strainer to catch the seeds. Key limes are notoriously seedy. You need half a cup of juice, which requires somewhere between twenty and twenty-five limes depending on their size and ripeness. If using bottled Key lime juice, measure half a cup and proceed.

5. 5

   Build the filling

   In a large bowl, whisk the egg yolks until they lighten slightly in color, about one minute. Add the sweetened condensed milk and whisk until completely smooth. The mixture will be thick and glossy. Add the Key lime juice in a steady stream, whisking constantly. Watch the transformation: the acid begins thickening the milk immediately. Fold in the zest. The filling should coat a spoon heavily.

6. 6

   Fill and bake

   Pour the filling into your cooled crust. It will mound slightly in the center. Bake at 350°F for 15 minutes. The filling is done when the edges are set but the center still wobbles like gelatin when you gently shake the pan. Do not overbake. The filling will continue to set as it cools.

   The brief bake ensures food safety and improves texture, but the pie would technically set without it. Old-timers sometimes skipped this step entirely.
7. 7

   Cool and chill

   Let the pie cool at room temperature for 30 minutes, then refrigerate uncovered until the filling is completely cold and firm, at least 4 hours or overnight. The filling will deepen to a pale greenish-yellow. Resist the urge to cover it with plastic until fully chilled, or you'll trap condensation.

8. 8

   Whip the cream

   When ready to serve, pour the cold heavy cream into a chilled bowl. Add powdered sugar and vanilla. Beat with a whisk or electric mixer until soft peaks form. The cream should billow and hold its shape but still look voluptuous, not stiff. Overwhipped cream turns grainy and begins its journey toward butter.

9. 9

   Top and serve

   Spread or pipe whipped cream over the chilled pie. Some prefer a modest layer; I vote for abundance. Garnish with paper-thin slices of Key lime if you have them. Cut with a sharp knife dipped in hot water, wiping clean between slices. Serve cold. This pie improves after a night in the refrigerator as the flavors marry and mellow.

Chef Tips

• •The difference between Key limes and Persian limes is not snobbery. Key limes have a distinct floral, almost perfumed quality that defines this pie. If you cannot find fresh Key limes, seek out Nellie and Joe's Famous Key West Lime Juice. It's what many Keys restaurants use, and there is no shame in it.
• •Sweetened condensed milk is not negotiable. It provides the sugar, the creaminess, and the proteins that react with the acid. Do not substitute evaporated milk, regular milk and sugar, or any other improvisation. The chemistry will fail you.
• •A graham cracker crust should taste like more than glue. Toast it. The difference between a raw crust and one that's been properly baked is the difference between adequate and excellent.
• •For the cleanest slices, freeze the pie for 20 minutes before cutting, then return it to the refrigerator to temper before serving. The filling cuts cleanly when very cold.
• •Save two tablespoons of graham cracker crumbs before making the crust. Sprinkled over the whipped cream, they add textural interest and visual honesty.

Advance Preparation

• •The filled pie can be made up to 2 days ahead and refrigerated, covered loosely with plastic wrap once fully chilled. Add whipped cream just before serving.
• •The graham cracker crust can be baked 3 days ahead, wrapped tightly, and stored at room temperature.
• •Key limes can be juiced and the juice frozen for up to 3 months. Thaw in the refrigerator before using. Zest does not freeze well; grate it fresh.

Frequently Asked Questions

Nutrition Information

1 serving (about 235g)