Tangy Key Lime Pie Cookie Bars Recipe

Desserts that combine a couple of favorites are always a delight, as they infuse novelty into familiar flavors. Mashed recipe developer Tess Le Moing shares these tangy key lime cookie bars which are an absolute treat. "This is a cross between a cookie and lemon bar (except we're using key limes)," she notes and describes, "They're soft, light, sweet, and vibrant with flavor."

Just like a classic key lime pie, these bars contain crushed up graham crackers along with some cinnamon, Le Moing explains. "The warmth from these ingredients balances out the tartness of the limes nicely," she says. Meanwhile, she notes that cream cheese "adds extra richness and salt to the cookies which I find helps temper the sweetness from the sugar and acidity from the limes." All in all, the result is the perfect balance of sweet and tangy flavors. 

For optimal serving results, Le Moing recommends chilling the bars until they're firm and cutting them with a large sharp knife. Pro tip: Wipe the blade between cuts for a cleaner slice. Store the bars in a sealed container at room temperature for up to three days. The lime zest might start to dull in hue, but it's still fine to eat.

For the cookie bars, you'll need all-purpose flour, graham cracker crumbs (about three graham cracker sheets), baking soda, kosher salt, ground cinnamon, granulated sugar, unsalted butter (melted), avocado oil, cream cheese (softened and cut into chunks), a large egg, a large egg yolk, key lime zest and juice, and vanilla extract. For the cream cheese frosting, you'll need cream cheese (softened to room temperature), salted butter (also softened to room temperature), confectioners' sugar, and vanilla extract.

Adjust the oven rack to the middle position and preheat the oven to 325 F.

Line a 13x9-inch baking pan with aluminum foil or parchment paper so extra foil hangs over all four sides of the pan. Grease with oil or butter.

Whisk the flour, graham cracker crumbs, baking soda, salt, and ground cinnamon in a mixing bowl.

Whisk the sugar, melted butter, oil, and cream cheese together in a second bowl (some lumps of cream cheese are okay).

Add the egg and yolk, lime zest and juice, and vanilla to the sugar mixture and whisk until smooth.

Pour the flour mixture into the wet mixture and fold with a rubber spatula until just combined.

Transfer the batter to the foil-lined pan, smoothing out the top with the spatula.

Bake until light golden brown and a toothpick inserted in the center comes out clean, about 35 to 40 minutes. Once out of the oven, cool completely in the pan for about 2 hours.

Place the cream cheese and butter in a mixing bowl.

With a hand mixer fitted with a whisk attachment, beat the cream cheese and butter on medium-high until creamy and no lumps remain.

Add the confectioners' sugar and vanilla extract.

Beat on low speed until the confectioners' sugar starts to combine then increase to high speed until combined and smooth.

Spread the frosting evenly over the cooled cookie bar.

Garnish with lime zest or green sugar sprinkles, if desired.

Using the foil or parchment overhang, lift the bars out of the pan and transfer them to a cutting board.

Cut into 24 pieces and serve.

These tangy key lime pie cookie bars boast a citrusy flavor in the cookie base, but the topping is a simple cream cheese frosting with a splash of vanilla. That leaves plenty of room to reinterpret it with novel ingredients if desired. Le Moing agrees and comments, "You can get creative and have fun with the frosting." If you want something a bit lighter than a cream cheese frosting, she recommends a glaze. Combine 1 cup of confectioners' sugar, 2 tablespoons water (or key lime juice), and some food coloring if desired. "The glaze will soak into the cookies slightly and add extra moisture and tang," Le Moing describes. 

Meanwhile, she suggests, "For a tropical twist and great dairy-free options, you can try a coconut cream frosting." To make this variation, whip chilled coconut milk or cream with powdered sugar and vanilla extract. "Of course, you can also omit the frosting altogether," she adds and shares, "Sometimes I like to mix equal parts melted butter and honey and brush it over top for a glossy shine on the cookies."

Key limes are a different variety than what you may be used to, but they're not wildly distinct. Le Moing describes them as "smaller with a thinner skin, slightly sweeter, more floral, and more aromatic." On the other hand, she notes, "Regular limes are larger, have thicker skin, [and are] more acidic and sharp without that slight sweetness of key limes." Originating in Southeast Asia, these tiny limes eventually made their way to the Florida Keys, which paints a clearer picture as to how the little citrus fruits got their name.

If you've never used key limes, it's a great excuse to try them. However, Le Moing says, "While the flavor will be slightly different, you can easily swap key limes for limes in this recipe if you can't [find] key limes in your grocery store." To make the swap, she recommends four to five medium-sized regular limes. "Most people won't be able to tell the difference, especially in a cookie," she adds.