2tablespoonspowdered sugar, plus more for dusting, see Recipe Notes
1large egg yolk
⅓cuplemon juice, freshly squeezed, from 2 lemons, see Recipe Notes
2tablespoonslime juice, freshly squeezed, from 1 lime, see Recipe Notes
1tablespoonzest, lemons and lime combined, see Recipe Notes
Preheat oven to to 325°F. Lightly coat a 9- x 9-inch baking pan with baking spray or butter. Line the baking pan with two pieces of parchment paper placed perpendicular to each other, covering all four sides and leaving a 2-inch overhang. Set aside.
Make the shortbread: In a medium bowl, mix the cooled melted butter, sugar, and salt. Add the flour and stir to combine.
Transfer the shortbread dough into the prepared baking pan. Press the dough evenly into the pan. Refrigerate the dough for 15 minutes.
Par-bake the shortbread for 18 to 22 minutes, or until the edges are lightly browned.
Make the filling: While the shortbread is baking, put the sugar and mint leaves in a small food processor and pulse until they’re finely blended. In a separate small bowl, sift the flour and powdered sugar together.
In a large mixing bowl, lightly beat the eggs until just combined. Add the mint sugar, flour mixture, lemon and lime juices and zest, and salt. Whisk until just combined.
Remove the par-baked shortbread from the oven and pierce the top it lightly with a fork (don’t go all the way through). Pour the curd filling onto the warm crust. Tap the pan a couple of times on the counter to release the trapped air.
Return the pan to the oven and bake for 18 to 20 minutes, or until the center is set and doesn’t jiggle when the pan is tapped. Turn off the oven a couple of minutes before the filling is entirely set and crack the oven door, allowing it to cool gradually.
Remove from the oven and cool counter for 1 hour, then chill for 1 hour more. Using a fine-mesh strainer, generously dust the bars with powdered sugar, then use the parchment paper as a sling to transfer to a cutting board.
Cut the slab into 16 squares. It’s best to dip the knife in hot water and wipe it dry between cuts to get neater squares.
Dust with more powdered sugar, if desired, then serve and enjoy bright lemony-limey-mint goodness!
Store the bars in the refrigerator for up to a week. They also can be frozen, cut into squares but with the powdered sugar dusting, for up to 4 months. Wrap the frozen lemon and lime squares in plastic wrap and store in an airtight bag. Thaw in the refrigerator for an hour or two, then dust with powdered sugar and serve.Using freshly juiced fruit will give the brightest flavor, but you can use bottled lemon or lime juice in a pinch.Zest the lemons and lime first, then juice them into a bowl measuring out enough to total ½ cup of juice. I also recommend straining the juices as you measure them to remove the seeds.Rather than making the mint sugar, you can chop the mint up very finely (mint confetti) and mix it in with the rest of the curd ingredients.Use binder clips to keep the parchment paper away from the curd while baking. Just clip them to the sides of the pan and bake away!Despite tapping out the air bubbles, they can still show up after baking. It happens when the eggs are over-whipped or the curd is over-baked. To prevent cracking, turn off the oven a couple of minutes before the filling is entirely set and crack the oven door, allowing it to cool gradually. If either of these things happen (and they did in my video), a good sprinkling of powdered sugar will cover them up.Lemon bars can melt the powdered sugar if it sits for too long. You can just sprinkle on some when you’re just about to serve them. Or better yet, get some non-melting Topping Sugar from King Arthur Flour.This recipe can be easily doubled. Press the shortbread dough into a 9- x 13-inch baking pan and par-bake for 20 to 22 minutes. Bake the lemon and lime curd filling for 22 to 26 minutes.