These moist, tender and tangy key lime pie bars have a cookie crumb crust, a custard filling and a simple lime curd topping. Make them days ahead of time, and they’ll still taste fresh!
These gluten free key lime pie bars start with a super simple graham cracker crust, filled with a key lime custard—and topped with a tart and tangy key lime curd. It's like lemon curd, but made with key lime juice instead. The custard filling is slightly less sweet than in my gluten free lemon bars, but it's only to make way for that gorgeous lime curd.
Since we are right at this very moment in the heart of the Florida key lime season, now is the time it should be easiest to find key limes in the grocery store. But if you can't find them or don't want to use them, no worries! Just use a combo of freshly squeezed regular lime juice and regular lemon juice. At the risk of sounding snooty, key limes have something of a more complex flavor than regular, or Persian, limes. They almost taste herbal. It's hard to explain. (I know; great job, food blogger.)
These moist, tender and tangy key lime pie bars can be made days and days ahead of time, since they keep incredibly well in a sealed container in the refrigerator. They must be properly chilled so they set, and then kept chilled through slicing. But once they're sliced, you can serve them chilled (my preference) or closer to room temperature. They're not going to wilt on you if they're not served right from the refrig.
The lime curd adds an extra special twist to these bars, but of course if you're not willing or able to make that layer, no problem. Just leave it out! Dust the top of the bars lightly with confectioners' sugar and maybe some more key lime (or regular lime) zest, and these bars will surely still impress!
Gluten Free Key Lime Pie Bars
For the crust
1 1/2 cups (225 g) gluten free cookie crumbs (I used my “Nabisco” GF Honey-Maid Grahams, from Classic Snacks)
6 tablespoons (84 g) unsalted butter, melted and cooled
1 egg white (25 g), at room temperature
For the custard filling
4 eggs (200 g, weighed out of shell)
3/4 cup (150 g) granulated sugar
3/4 teaspoon baking powder
2/3 cup freshly squeezed key lime juice (from about 1 pound key limes)*
2/3 cup (93 g) basic gum-free gluten free flour blend
For the lime curd
1/2 cup (100 g) granulated sugar
4 1/2 teaspoons (14 g) basic gum-free gluten free flour blend
4 1/2 teaspoons (14 g) cornstarch
3/4 cup (6 fluid ounces) milk (any kind), at room temperature
1/4 cup (2 fluid ounces) freshly-squeezed key lime juice
Finely grated zest of 1 lime
2 egg yolks (50 g), at room temperature
1 tablespoon (14 g) unsalted butter, chopped
2 drops green liquid food coloring (so very optional)
Key limes, for garnishing (optional)
*A note about key limes: If you can’t find or don’t want to use key limes, replace the key lime juice with half (1/3 cup) freshly-squeezed lemon juice and half (1/3 cup) freshly squeezed lime juice.
Preheat your oven to 325°F. Line an 8-inch square baking pan with overhung, crisscrossed pieces of unbleached parchment paper and set it aside.
Prepare the crust. In a medium-size bowl, place the cookie crumbs, then the melted butter and egg white, and mix until all of the crumbs are moistened. Place the cookie crumb mixture in the prepared pan and press firmly into an even layer on the bottom of the pan and very slightly up the sides. Set the pan aside.
Prepare the custard filling. In a medium-sized bowl, place the eggs, granulated sugar, baking powder, key lime juice and flour, whisking vigorously to combine after each addition. Pour the custard mixture on top of the prepared crust. Place the pan in the center of the oven and bake until just set (20 to 25 minutes). The custard is set when it does not jiggle more than a tiny bit in the center when the pan is shaken gently back and forth. Remove from the oven and allow the bars to cool in the pan for about 20 minutes before placing in the refrigerator to chill.
Make the lime curd. In a medium-size, heavy-bottom saucepan, place the sugar, flour blend, cornstarch, 1/2 cup of the milk, and lime juice and zest, and whisk to combine well. Place the egg yolks and the remaining 1/4 cup milk in a medium-size heat-safe bowl, whisk to combine well, and set the bowl next to the stovetop. Place the saucepan over medium heat and bring to a simmer, whisking constantly. In a very, very slow trickle, pour about half of the hot milk mixture into the bowl with the egg yolk mixture, whisking constantly. This step will temper the eggs so they do not scramble. Pour the warm egg yolk and milk mixture into the saucepan with the remaining hot milk mixture, and return to the heat. Cook over medium-high heat, whisking constantly, until the mixture has thickened enough that the whisk leaves a very visible trail in the mixture (about 4 minutes). Remove from the heat, add the tablespoon of butter and the very optional food coloring, and whisk to combine. Transfer the lime curd to a separate, heat-safe bowl and cover with plastic wrap placed directly on the surface of the curd to prevent a skin from forming. Allow it to cool for about 20 minutes, or until no longer hot to the touch.
Finish the bars. Remove the baking pan from the refrigerator, uncover the bowl of lime curd and scrape the cooled curd on top of the key lime bars while they are still in the pan. Using an offset spatula or large knife, spread the lime curd into an even layer. Place the pan in the refrigerator to chill until firm, about 2 hours and up to overnight. Remove the bars from the pan by running a butter knife or thin spatula around the perimeter of the baking dish, and then lifting the bars out of the pan by the overhung pieces of parchment paper. Slice into 9 or 12 squares with a large knife. Garnish each square with a slice of a key lime. Serve chilled.
Adapted from my Lemon Bars.