Preheat oven to 350°F (175°C) and line an 8×8-inch pan with parchment paper.
In a bowl, mix gluten-free flour, sugar, and salt. Cut in cold butter until crumbly.
Press mixture firmly into the pan and bake for 18–20 minutes, until lightly golden.
In another bowl, whisk sugar, eggs, lemon juice, lemon zest, cornstarch, and salt until smooth.
Pour filling over the hot crust immediately after removing it from the oven.
Return pan to oven and bake for 22–25 minutes, until the center is just set.
Cool completely, then refrigerate for at least 2 hours before slicing.
Dust with powdered sugar before serving.
