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Key Lime Bars Recipe: How to Make Key Lime Squares

Written by MasterClass

Last updated: Mar 31, 2022 • 3 min read

Key lime bars capture every ounce of key lime pie’s balanced, puckering sweetness—in miniature.

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What Are Key Lime Bars?

Key lime bars are individually portioned desserts in the style of key lime pie, a classic American dessert with a creamy filling made from key lime juice, egg yolks, and sweetened condensed milk, served in a graham cracker pie crust. Like the best key lime pie recipes, key lime bars allow for various toppings.

Top the square bars with meringue, whipped cream, or, like a lemon bar, a simple coat of powdered sugar.

Key Limes vs. Limes: What Are the Differences?

Here’s how key limes differ from the regular limes that line the shelves of most grocery stores:

  • Color: Ripe key limes have a yellow-green hue, while standard limes—also known as Persian limes—are deep green.
  • Flavor: Overall, key limes are more fragrant than other varieties, with lightly tart sweetness and less pronounced acidity. (Persian limes have a more bracing citrus flavor.) The mild tartness and floral scent of key limes make them ideal for desserts like key lime cheesecake.
  • Origin: Persian limes likely first arrived in the Mediterranean from Persia (modern-day Iran), and their popularity spread from there. In the summertime, key limes grow wild throughout the Florida Keys region of the United States.
  • Size: Key limes are smaller than Persian limes, with more seeds and a thinner, softer rind.

3 Tips for Making Key Lime Bars

Show up with key lime pie bars to your next potluck or party, and you’ll likely be the most popular person in the room. Here’s what to remember:

  1. 1. Use fresh key lime juice. Use fresh key limes for both juice and zest. If you can’t find key limes, use regular lime juice and zest, but avoid bottled lime juice and artificial lime flavoring. The acidity and delicate floral notes of fresh limes are unparalleled, and fresh lime zest infuses the filling with lime flavor. Here’s how to juice a lime.
  2. 2. Choose your crust. Key lime bars consist of a lime curd filling atop a crumbly cookie base. For the base, choose between a classic graham cracker crust or a buttery shortbread crust. If you like, add chopped pecans or pistachios for extra texture. Whichever you choose, make sure the baked crust has cooled before assembling the bars.
  3. 3. Chill the pie completely before slicing it into bars. To preserve each bar’s neat layers, chill the filling until it’s completely set. If you’re making the pie in advance, place the entire pan in the refrigerator—with a sheet of plastic wrap gently pressed onto the surface—the night before serving.

Easy Key Lime Bars Recipe

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makes

1 9x13 baking dish (12–20 bars, depending on size)

prep time

15 min

total time

45 min

cook time

30 min

Ingredients

For the graham cracker crust:

For the key lime filling and assembly:

Note: The total time does not include 1 hour of inactive time.

Make the crust:

  1. 1

    Preheat the oven to 325 degrees Fahrenheit.

  2. 2

    Line a 9x13-inch rectangular baking pan with parchment paper so that it hangs over the sides.

  3. 3

    In the bowl of a food processor, pulse the graham crackers until they resemble coarse pebbles. (You should have about 3 cups, but add more if you like a thicker crust.)

  4. 4

    In a medium bowl, combine the graham cracker crumbs and melted butter. The mixture should be wet enough to hold together when pressed.

  5. 5

    Using a rubber spatula, press the crumbs into an even layer over the bottom of the prepared pan.

  6. 6

    Bake the crust until firm, about 15 minutes.

  7. 7

    Let the crust cool for at least 10 minutes before filling.

Make the filling and assemble the bars:

  1. 1

    In a large bowl, whisk the 6 egg yolks with the beaten whole eggs until thickened, about 1–2 minutes.

  2. 2

    Add the condensed milk, then whisk in the lime juice and zest.

  3. 3

    In another large mixing bowl or the bowl of an electric mixer, beat the egg whites until stiff peaks form.

  4. 4

    Fold one-third of the beaten whites into the custard, then fold in the remaining whites.

  5. 5

    Pour the filling over the crust and smooth the top.

  6. 6

    Bake until the custard is just barely set, about 10 minutes.

  7. 7

    Transfer the pan to a wire rack and let it cool completely. Place the pan in the refrigerator to chill for at least 1 hour and up to overnight.

  8. 8

    Just before slicing, sift the confectioners’ sugar over the bars.

  9. 9

    Use a sharp knife to portion into squares or rectangles, wiping down the knife with warm water in between slices.

  10. 10

    Top each bar with a lime wheel and serve with a dollop of whipped cream if desired.

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