01 - Preheat oven to 350°F. Line a 9x9-inch baking pan with parchment paper, allowing an overhang for easy removal.
02 - In a large bowl, cream together softened butter and granulated sugar until light and fluffy. Add flour and salt, mixing until just combined.
03 - Press dough evenly into the prepared pan bottom. Bake for 18-20 minutes until edges are lightly golden.
04 - Whisk together sugar and flour in a separate bowl. Add eggs, grapefruit juice, grapefruit zest, and lemon juice. Whisk until smooth and fully combined.
05 - Pour filling mixture over the hot crust immediately after removing from oven.
06 - Return pan to oven and bake for 18-22 minutes until center is just set with minimal jiggle.
07 - Let cool completely in pan. Lift out using parchment overhang and cut into bars.
08 - Dust with powdered sugar just before serving.