1 2/3 cups (233 g) basic gum-free gluten free flour blend (superfine white rice flour + potato starch + tapioca starch/flour)
1/2 cup (58 g) confectioners’ sugar, plus more for dusting
1/2 teaspoon kosher salt
Zest of 1 large lemon
9 tablespoons (126g) unsalted butter, melted and cooled
4 eggs (200 g, weighed out of shell), at room temperature
1 cup (200 g) granulated sugar
3/4 teaspoon baking powder
2/3 cup freshly squeezed lemon juice (juice of 4 to 5 lemons)
Preheat your oven to 325°F. Grease an 8-inch square baking pan, line with criss-crossed pieces of parchment paper that overhang the sides, and grease the parchment paper. Set the pan aside.
Make the crust. In a medium-sized bowl, combine 1 cup (140 g) of the flour, confectioners’ sugar, salt and lemon zest and whisk to combine, breaking up any clumps of lemon zest. Add the butter and mix with a fork until well-combined. Press the mixture into the bottom of the prepared baking dish in an even layer. Place the baking dish in the center of the preheated oven and bake for about 15 minutes or until firm. Remove from the oven and allow to cool briefly.
Make the custard layer. In a medium-sized bowl, place the eggs, granulated sugar, baking powder, lemon juice and remaining 2/3 cup (93 g) flour, whisking vigorously to combine after each addition. Pour the custard mixture into the baked crust and return the pan to the center of the oven. Bake until just set (about 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 the pan from the oven and allow to cool in the pan for about 20 minutes.
Place 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. Dust lightly with confectioners sugar, and slice into 9 or 12 squares with a large knife. Serve chilled.
Recipe originally published in 2011, updated in 2015 and modified again (photos, video, text mostly new) in 2019.