01 -
Preheat the oven to 350°F (180°C). Line a 9-inch square baking pan with parchment paper, leaving an overhang on two sides for easy lifting.
02 -
Stir together the melted butter, sugar, flour, and salt until a soft dough forms. Press the dough firmly and evenly into the bottom of the prepared pan. Bake for 15 minutes until just set and pale golden at the edges.
03 -
In a large bowl, beat the eggs with the sugar until combined. Mix in the grapefruit juice, lemon juice, zest, flour, and salt until the batter is smooth.
04 -
Pour the filling over the warm crust. Bake for 20 to 25 minutes until the filling is set around the edges and the center has only a slight jiggle.
05 -
Let the bars cool to room temperature in the pan, then refrigerate for at least 2 hours. Use the parchment overhang to lift them out, and slice into 16 squares.