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My mother set her key lime pie on the table at a family reunion, and a man from up north looked at it and said it couldn’t be key lime, because key lime pie is green. She cut him a slice and let him find out for himself. He had two, and he never said the word green again. Real key lime pie is pale yellow. Only the ones with food coloring are green. Key lime pie is even the official state pie of Florida, where it comes from, and down there nobody would dream of making it green.
The filling is three things: sweetened condensed milk, egg yolks and lime juice, with a little zest for perfume. The color comes from the egg yolks and the cream of the condensed milk, because key lime juice itself is pale, almost clear. And the way it sets is a little kitchen magic: the acid in the lime juice thickens the condensed milk right there in the bowl, and a short bake sets the yolks so the pie slices clean and is safe to eat.
Here is the whole recipe, with the buttery graham cracker crust, why the pie is pale yellow, and exactly how to make it set firm instead of runny.
Why this key lime pie works
- Condensed milk and lime juice. The acid in the juice thickens the milk proteins, which is why the filling turns thick as you whisk.
- Egg yolks. They give the pale yellow color and the custardy body, and they set firm in the oven.
- A short bake. Fifteen minutes is enough to set the yolks without making the filling rubbery or cracked.
- A pre-baked crust. Baking the graham crust first keeps it crisp and stops it from crumbling when you slice.
- A long chill. Four hours in the refrigerator finishes the set and gives clean, smooth slices.
Ingredients
Makes one 9 inch pie, 8 slices. The measurements are in US cups with grams in brackets.
For the graham cracker crust
- 1 1/2 cups graham cracker crumbs (150g), about 10 full sheets
- 1/3 cup granulated sugar (65g)
- 6 tablespoons unsalted butter, melted (85g)
- A pinch of fine salt
For the filling
- 4 large egg yolks
- 1 can (14 ounces, 397g) sweetened condensed milk
- 1/2 cup key lime juice (120ml), fresh or bottled
- 1 tablespoon finely grated lime zest
For the topping
- 1 cup cold heavy cream (240ml)
- 2 tablespoons powdered sugar (15g)
- 1/2 teaspoon vanilla extract
- Lime slices or extra zest, to decorate
Fresh key limes are small and fiddly, about 20 for half a cup of juice. Bottled key lime juice works very well, and regular Persian limes make a fine pie too, just a little less floral. Use regular lime zest either way; key lime zest is too thin to grate well.
How to make key lime pie
- Heat the oven to 350 degrees (175°C).
- Stir the graham cracker crumbs, sugar, salt and melted butter together until the crumbs look like wet sand.
- Press the crumbs firmly and evenly over the bottom and up the sides of a 9 inch pie plate, using the bottom of a measuring cup to pack them tight.
- Bake the crust for 10 minutes, until fragrant and lightly golden. Set it on a rack to cool for at least 15 minutes. Leave the oven on.
- In a large bowl, whisk the egg yolks and lime zest for about 1 minute, until the yolks turn pale.
- Whisk in the condensed milk until smooth.
- Pour in the lime juice a little at a time, whisking. You will feel the mixture thicken as the juice goes in. Whisk until smooth and creamy.
- Pour the filling into the cooled crust and smooth the top.
- Bake for 15 to 17 minutes, until the edges are set and the center still has a slight wobble when you nudge the pan.
- Cool the pie on a rack for 30 minutes, then refrigerate, uncovered at first and then loosely covered, for at least 4 hours or overnight, until cold and firm.
- Just before serving, whip the cold cream with the powdered sugar and vanilla to soft peaks. Spread or pipe it over the pie, decorate with lime slices or zest, and slice with a knife dipped in hot water and wiped dry.
Tips that make the difference
- Do not skip the bake. It sets the yolks, so the pie slices cleanly and the eggs are cooked through.
- Take the pie out while the center still wobbles. It firms up completely as it chills; overbaked filling cracks and turns grainy.
- Zest the limes before you juice them. It is almost impossible the other way around.
- For the cleanest slices, chill the pie overnight and wipe the knife between every cut.
Variations
- Meringue top. Whip the 4 leftover egg whites with 1/2 cup sugar (100g) to stiff peaks, spread over the warm baked pie to the crust, and bake 10 to 12 minutes more until golden.
- Thicker pie. For a deep-dish 9 inch pie, double the filling and bake 20 to 25 minutes.
- Key lime bars. Press the crust into an 8 inch square pan, use the same filling, and cut into squares.
- Lemon. Use fresh lemon juice and lemon zest for a pale, bright lemon icebox-style pie.
Storage and make-ahead
Keep the pie covered in the refrigerator for up to 3 days. Add the whipped cream on the day you serve it.
Key lime pie freezes well without the topping. Wrap the chilled pie and freeze for up to a month; thaw overnight in the refrigerator.
Some people love it half frozen on a hot day, straight from the freezer.
Frequently asked questions
Why is key lime pie yellow and not green?
The color comes from the egg yolks and the condensed milk. Key lime juice is pale, almost clear, so a real key lime pie is pale yellow. Green key lime pies are colored.
Why didn’t my key lime pie set?
Usually it was underbaked, or it was not chilled long enough. Bake until the edges are set with only a slight wobble in the middle, then chill for at least 4 hours.
Can I use regular limes?
Yes. Persian limes make a slightly sharper, less floral pie, but it sets and tastes wonderful.
Do I have to bake key lime pie?
Old no-bake versions relied on the lime juice alone to thicken the filling, but baking sets the yolks properly and is the safe way to make it.
Bring it out cold on a warm evening, let somebody tell you it ought to be green, and hand them a fork.
Key Lime Pie (Pale Yellow, Never Green, in a Graham Cracker Crust)
Classic key lime pie: a smooth, sweet-tart filling of sweetened condensed milk, egg yolks and key lime juice baked briefly in a buttery graham cracker crust, chilled until firm and topped with whipped cream. Naturally pale yellow, never green.
Ingredients
- 1 1/2 cups graham cracker crumbs (150g), about 10 full sheets
- 1/3 cup granulated sugar
- 6 tablespoons unsalted butter, melted
- A pinch of fine salt
- 4 large egg yolks
- 1 can (14 ounces, 397g) sweetened condensed milk
- 1/2 cup key lime juice (120ml), fresh or bottled
- 1 tablespoon finely grated lime zest
- 1 cup cold heavy cream
- 2 tablespoons powdered sugar
- 1/2 teaspoon vanilla extract
- Lime slices or extra zest, to decorate
Instructions
- Heat the oven to 350 degrees (175°C).
- Stir the graham cracker crumbs, sugar, salt and melted butter together until the crumbs look like wet sand.
- Press the crumbs firmly and evenly over the bottom and up the sides of a 9 inch pie plate, using the bottom of a measuring cup to pack them tight.
- Bake the crust for 10 minutes, until fragrant and lightly golden. Set it on a rack to cool for at least 15 minutes. Leave the oven on.
- In a large bowl, whisk the egg yolks and lime zest for about 1 minute, until the yolks turn pale.
- Whisk in the condensed milk until smooth.
- Pour in the lime juice a little at a time, whisking. You will feel the mixture thicken as the juice goes in. Whisk until smooth and creamy.
- Pour the filling into the cooled crust and smooth the top.
- Bake for 15 to 17 minutes, until the edges are set and the center still has a slight wobble when you nudge the pan.
- Cool the pie on a rack for 30 minutes, then refrigerate, uncovered at first and then loosely covered, for at least 4 hours or overnight, until cold and firm.
- Just before serving, whip the cold cream with the powdered sugar and vanilla to soft peaks. Spread or pipe it over the pie, decorate with lime slices or zest, and slice with a knife dipped in hot water and wiped dry.
