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 dough forms.
03 - Press dough evenly into prepared pan bottom. 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 lime mixture over hot crust. Return to oven and bake for 15-18 minutes until center is set and no longer jiggles.
06 - Let cool completely in pan on wire rack. Refrigerate for at least 1 hour before slicing.
07 - Dust with powdered sugar, cut into bars, and serve.