01 - Preheat oven to 350°F. Line a 9x9-inch baking pan with parchment paper, allowing overhang for easy removal of the bars.
02 - Cream softened butter and granulated sugar in a large bowl until light and fluffy. Blend in flour and salt, mixing until just combined into a dough.
03 - Press dough evenly into the bottom of the prepared pan. Bake for 18-20 minutes until edges are lightly golden.
04 - Whisk sugar and flour together in a separate bowl. Add eggs, grapefruit juice, grapefruit zest, and lemon juice. Whisk until smooth and fully combined.
05 - Pour the filling mixture over the hot crust immediately after removing from the oven.
06 - Return pan to oven and bake for 18-22 minutes until the center is just set and no longer jiggles excessively.
07 - Let cool completely in the pan. Once cooled, lift out using the parchment overhang and cut into bars.
08 - Dust with powdered sugar just before serving.