Preheat your oven to 350F and line a 9×13 inch baking dish with parchment paper.
In a large bowl, whisk together 2 1/2 cups of the gluten-free flour, powdered sugar, and salt.
Add the melted butter to the dry mixture and stir until a uniform dough forms.
Press the dough firmly and evenly into the bottom of the prepared baking pan.
Bake the crust for 20 minutes until lightly golden.
While the crust bakes, combine the granulated sugar and lemon zest in a bowl, rubbing them together until fragrant.
Whisk in the remaining 1/2 cup of gluten-free flour.
Add the room temperature eggs and fresh lemon juice, whisking until the mixture is smooth and emulsified.
Pour the filling over the hot crust once it comes out of the oven.
Reduce oven temperature to 325F and bake for an additional 25 minutes or until the center is set.
Allow to cool completely to room temperature before refrigerating for at least 2 hours to ensure a perfect slice.