Preheat your oven to 350°F (175°C) and prepare an 11x7-inch baking dish by greasing it or lining it with parchment paper.

In a food processor, combine all-purpose flour, powdered sugar, and salt. Add cold, cubed unsalted butter and pulse until the mixture resembles coarse crumbs. Press this crumbly dough into the bottom of your prepared dish. Bake for 18-20 minutes until golden brown, then cool slightly.

In a mixing bowl, whisk together granulated sugar and a tablespoon of flour. Gradually add in the large eggs, mixing well after each addition. Fold in the grapefruit zest and juice, mixing in pink food coloring if desired.

Pour the grapefruit filling over the warm crust and bake for an additional 20 minutes until the filling has set but still jiggles slightly.

After baking, let it cool in the pan for about an hour. Transfer to the refrigerator to chill for at least 1-2 hours.

Once chilled, lift the bars out of the pan, cut into squares, and dust with powdered sugar before serving.