Place an oven rack in the center of the oven; preheat to 350°F. Line an 8-inch square baking dish with parchment paper (extending it over the sides so the bars are easier to transfer). Melt the butter in a large bowl in the microwave (or melt in a small pot on the stove, then transfer to a large bowl). Add the granulated sugar, vanilla powder, and a pinch of salt; whisk to combine. Add the all-purpose four, almond flour, and rice flour. Stir to thoroughly combine. Transfer to the baking dish. Using the flat bottom of a glass or measuring cup, press into an even layer. Bake 20 to 22 minutes, or until the crust begins to brown around the edges. Remove from the oven.

Carefully top the baked shortbread with the lemon curd; spread into an even layer. Bake 24 to 26 minutes, or until the curd is set. Remove from the oven. Refrigerate about 1 hour, or until cool.

Once cooled, transfer (in the parchment) to a cutting board; cut into equal-sized squares. Use a small sieve (or tablespoon) to sprinkle with as much of the powdered sugar as you’d like. Enjoy!