01 - Preheat oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving overhang for easy removal.
02 - In a medium bowl, cream together softened butter and granulated sugar until light and fluffy. Mix in flour and salt until a dough forms.
03 - Press the dough evenly into the bottom of the prepared pan. Bake for 18–20 minutes until lightly golden.
04 - In a large bowl, whisk together sugar and flour. Add eggs, lime juice, and lime zest. Whisk until smooth. Add green food coloring if desired.
05 - Pour the lime mixture over the hot crust. Return to the oven and bake for 15–18 minutes until the center is set and no longer jiggles.
06 - Let cool completely in the pan on a wire rack. Refrigerate for at least 1 hour before slicing.
07 - Dust with powdered sugar, cut into bars, and serve.