Key Lime Pie must have a graham cracker crust (the thicker the better) and a custard filling (not a mousse); it is unpolluted by gelatin, and is never, ever green (no matter what kind of limes you use – we’ll get to that in a minute). It gets its silky texture and sunny yellow color from egg yolks, and its bracing tartness from grated lime zest. The sky-high pouf of whipped cream is optional but highly recommended.
I’m obviously opinionated about a lot of things when it comes to Key Lime Pie, but surprisingly open-minded about the limes. So let’s talk about those. To stay true to the classic, you should use Key lime juice. Now you have a choice: this can either be the easiest pie you’ll ever make, or a marathon workout for your arms and your patience, depending on whether or not you insist on using fresh, teeny tiny Key limes. You can buy bottled Key lime juice (like this one carried by King Arthur Flour) and as long as it’s real juice, not imitation, you won’t be able to tell the difference.
If you can find fresh Key limes and want to use them, here are a couple of tips: juice them at room temperature, not cold, and don’t cut them in half like you would a larger lime, instead cut a deep X in one end, spread the cut open, and juice from there.
You can also use Persian limes, the large green ones you find at any grocery store. Purists would say that you’re not allowed to call it Key Lime Pie then, so don’t, but make the pie anyway and call it whatever you want, it will be delicious. (And yellow. If the custard is green, it’s artificial.)
I use bottled juice, plus one whole green lime for the zest that gets sprinkled over the finished pie and the whipped cream topping for a garnish. If you like your Key Lime Pie extra tart (like I do), zest a little extra to stir into the filling. I’ve given measurements for the zest in the recipe, but I know measuring citrus zest is a pain; if you plan to include zest in the filling, zest the entire lime. If you don’t, zest half of it. Close enough.
The graham cracker crust is John’s favorite part and I make it extra thick, giving it equal status with the filling so that each bite is a perfect balance of sweet sandy crumbs and tart creamy custard. When shaping the crust, I use the edge of a small measuring cup to press the crumbs into the bottom inside edge, for neater slices.
Do not be tempted to take a shortcut and use a packaged, pre-made graham cracker crust. These are way too thin and have a stale taste. Since graham cracker crusts are so easy to make, and the flavor and texture of homemade ones is so far superior, there’s no reason to compromise.
If you’re serving the whole pie at once, you could swoop all the whipped cream in a big pile in the center of the pie for a dramatic presentation. Since we never finish the whole pie in one sitting, I dollop each individual piece with whipped cream, store the remainder of the pie plain, and then whip fresh cream the next day for the leftovers. I think I actually prefer the way the slices of pie look with that cumulus cloud of whipped cream in the center, framed by the bright yellow custard.
Making this ahead and what to do with leftovers:
- Key Lime Pie keeps well, so go ahead and make it the day before, and keep leftovers for 3 days. (Maybe longer – I wouldn’t know because we’ve never been able to keep from finishing it in 3 days.)
- If you use bottled juice you’ll have plenty left over for another pie or even two. If you don’t want that much pie (what’s wrong with you?), use the juice in any other recipe calling for lime juice. For example, Margaritas! If you can’t use the juice within 5 days of opening the bottle, pour the leftover amount into a zip-lock bag and freeze it for up to several months.
Key Lime Pie
Ingredients
- 8 tablespoons (½ cup, 4 ounces, or 1 stick) butter, either salted or unsalted
- 13 whole rectangular graham cracker sheets (about 6 7/8 ounces)
- 1 tablespoon granulated sugar
- Kosher salt
- 4 large egg yolks
- One 14-ounce can sweetened condensed milk
- ½ cup Key lime juice
- ¾ to 1½ teaspoons finely grated zest from a conventional (Persian) lime, to taste
- ¾ cup heavy cream
- 1 tablespoon plus one teaspoon confectioner’s sugar
Directions
- Step 1 Heat the oven to 350.
- Step 2 Melt the butter in a small saucepan.
- Step 3 Break up the graham crackers with your hands and put them in the bowl of a food processor, along with the granulated sugar and one large pinch of kosher salt if you used salted butter, two if you used unsalted. Process the mixture into fine crumbs. Dump the crumbs into a bowl and add the melted butter. Toss with a fork until the crumbs are evenly moistened and look like wet sand. Press the crumbs into a 9” pie plate to form a thick crust.
- Step 4 Bake the crust for 10 minutes.
- Step 5 While the crust is baking, make the filling. Combine the egg yolks, sweetened condensed milk and lime juice in a bowl or large liquid measuring cup and whisk until smooth. If you want the filling to be extra tart and lime-y, add ¾ teaspoon of the grated lime zest (optional), and whisk it in.
- Step 6 When the crust is done baking, immediately pour the filling in and return the pie to the oven to cook for 15 more minutes. Remove the pie to a rack to cool completely.
- Step 7 Sprinkle about half of the remaining grated lime zest evenly over the surface of the cooled pie. Chill the pie, uncovered, for at least four hours, or overnight.
- Step 8 For serving, whip the heavy cream with the confectioner’s sugar into soft peaks. Dollop the sweetened whipped cream over the pie and sprinkle the whipped cream with the last of the lime zest.
