How to Make Key Lime Pie from Scratch

Key lime pie pairs a crisp, buttery graham cracker crust with a smooth filling that is sweet, tart, and gently citrusy. This recipe makes one 9-inch pie, usually enough for 8 slices. Gather the ingredients and allow time for baking and chilling; the pie needs several hours in the refrigerator to firm up.

What You’ll Need

9-inch pie plate
Food processor or a sturdy bag and rolling pin for crushing crackers
Mixing bowls, measuring cups and spoons, whisk, and citrus juicer
Instant-read thermometer, optional but useful for checking the filling
1 1/2 cups (about 150 g) finely crushed graham crackers, roughly 10 to 12 full sheets
5 tablespoons unsalted butter, melted
2 tablespoons granulated sugar
4 large egg yolks
1 can (14 ounces) sweetened condensed milk
1/2 cup key lime juice, freshly squeezed or bottled
1 tablespoon finely grated key lime zest, optional
Whipped cream and thin lime slices, optional, for serving

Step-by-Step

Heat the oven. Set a rack in the center and preheat the oven to 350°F. Make sure the pie plate is clean and dry. Baking the crust first helps it hold together beneath the moist filling.
Crush the crackers. Process the graham crackers into fine, even crumbs. If using a bag, seal it and crush the crackers with a rolling pin. Measure 1 1/2 cups after crushing; large pieces can make the crust crumble.
Mix and press the crust. Stir the crumbs with the melted butter and sugar until the mixture resembles damp sand. Tip it into the pie plate. Press firmly and evenly across the bottom and up the sides, using the flat bottom of a measuring cup to compact it.
Prebake the crust. Bake for 8 to 10 minutes, until fragrant and lightly browned. Set it on a rack to cool while you prepare the filling. Leave the oven on. A warm crust is fine, but pouring filling into a very hot plate may make it harder to handle.
Whisk the yolks. In a medium bowl, whisk the egg yolks until smooth and slightly thickened, about 1 minute. Avoid whipping in lots of air; bubbles can leave an uneven surface.
Make the filling. Whisk in the sweetened condensed milk until combined, then add the lime juice and zest, if using. Mix just until smooth. The filling thickens as the citrus reacts with the milk, but it still needs baking to set safely and evenly.
Fill the crust. Pour the mixture into the cooled or slightly warm crust and spread it gently to the edges. Tap the plate lightly on the counter to release large air bubbles.
Bake until just set. Bake at 350°F for about 15 to 18 minutes. The outer portion should look set while the center retains a small, gentle wobble; it should not slosh. For a temperature check, insert a food thermometer in the center without touching the plate. The egg-based filling should reach 160°F. If it has not, continue baking in short intervals and check again. Do not wait for the center to become completely firm in the oven, as it will continue setting as it cools.
Cool and chill. Cool the pie on a rack until it is no longer hot, then cover and refrigerate for at least 4 hours, preferably overnight. Chilling firms the filling and makes clean slices possible. Keep it refrigerated rather than leaving it out for an extended period.
Serve cold. Add whipped cream and lime slices just before serving, if desired. For neat slices, use a sharp knife wiped clean between cuts. Return leftovers promptly to the refrigerator.

Common Mistakes

Using too much lime juice: More juice may sound like a way to make the pie tangier, but it can disrupt the filling’s balance and texture. Measure 1/2 cup; add zest for a more fragrant lime flavor instead.

Making a loose crust: Crumbs that are too coarse or not pressed firmly can fall apart. Crush them finely, mix until evenly moistened, and compact the base and sides before baking.

Overbaking: A fully firm center in the oven often means the pie will be dry or develop cracks after cooling. Take it out when the edges are set and the middle has only a slight wobble, while ensuring the egg filling reaches 160°F.

Slicing before chilling: Warm filling is soft and may run. Give the pie at least 4 hours in the refrigerator; longer chilling improves its structure.

Confusing key limes with regular limes: Key limes are small and aromatic, but they can be time-consuming to juice. Bottled key lime juice is a practical substitute. Regular Persian lime juice also works, though the flavor will be a little different.

Tips

Roll limes on the counter with gentle pressure before cutting them; this can make them easier to juice.
Zest the fruit before juicing. Use only the colored outer peel, not the bitter white pith.
For a stronger citrus aroma without extra liquid, mix finely grated zest into the filling.
Press crust crumbs slightly up the rim, but keep the thickness consistent so thin areas do not burn.
Set the pie plate on a baking sheet if the crust is fragile or the filling is close to the rim. This also makes it easier to move in and out of the oven.
For a topping that holds its shape, add whipped cream shortly before serving rather than before chilling the whole pie.

Troubleshooting

The filling is still very loose after cooling: It may be underbaked or not fully chilled. Refrigerate it for several more hours first. If it remains liquid, it was likely not baked enough; the next time, check the center with a food thermometer and bake until it reaches 160°F.

The top has small cracks: The pie may have baked too long or cooled too quickly. Small cracks are harmless and can be covered with whipped cream. Next time, remove it when the center still has a slight wobble and let it cool gradually on a rack.

The crust crumbles when cut: It may have needed more butter, firmer pressing, or additional prebaking. Measure the butter accurately and compact the crumb mixture well before baking. Let the pie chill fully before cutting.

The pie tastes too sweet or not tart enough: The balance depends partly on the juice. Use fresh or bottled key lime juice and add zest for more lime character. Avoid changing the juice quantity substantially, since it affects the filling’s consistency.

Frequently Asked Questions

Can I use regular lime juice instead of key lime juice?

Yes. Regular Persian lime juice works in the same measured amount, though key limes have a distinctive, often more floral aroma. Bottled key lime juice is another convenient option.

Do I have to prebake the graham cracker crust?

Prebaking helps the crust turn crisp and stay intact under the filling. Bake it for 8 to 10 minutes before adding the filling.

Can I make key lime pie ahead?

Yes. Make it a day ahead and keep it covered in the refrigerator. Add whipped cream and fresh garnishes close to serving time.

How should I store leftover key lime pie?

Cover and refrigerate leftovers promptly, and use them within 3 to 4 days. Because this pie contains eggs and dairy, do not leave it at room temperature for more than 2 hours, or more than 1 hour when the temperature is above 90°F.

Can I freeze key lime pie?

You can freeze the pie, tightly wrapped, for up to about 1 month for best quality. Thaw it in the refrigerator; add whipped cream after thawing. Its texture may be slightly softer than a freshly chilled pie.

Why is my pie still wobbly after baking?

A small wobble in the center is expected because the filling firms as it cools and chills. If the center sloshes or has not reached 160°F, bake it longer in short intervals and check again with a food thermometer.

Further reading: USDA FoodSafety.gov. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.