Preheat the oven to 350°F (175°C).Line a 9×13-inch baking pan with parchment paper.Mix the flour, powdered sugar, and salt for the crust.Cut in the butter until the mixture resembles coarse crumbs.Press evenly into the prepared pan.Bake for 20 minutes, until lightly golden.Meanwhile, whisk together the sugar, flour, eggs, lemon juice, and zest.Pour the filling over the hot crust.Bake for another 22–25 minutes, until the center is just set.Cool completely, then refrigerate for 2 hours.Dust generously with powdered sugar before slicing.