Begin by squeezing the lemons to extract the juice, then strain it to ensure it's smooth and measure out 1 cup.
In a mixing container, combine the grapefruit juice, lemon juice, and granulated sugar, stirring until the sugar is fully dissolved.
Add the gin, Campari, and grapefruit cordial to the mixture, and stir well to combine all the ingredients.
Serve the cordial over ice and garnish with a twist of grapefruit zest for added flavor.
