In a cocktail shaker, place the sugar, grapefruit peel and salt. Muddle until the grapefruit is fragrant and the sugar is clumping.
Add the gin, water, and a big scoop of ice. Snap on the lid, then shake until the outside of the container is cold.
Fill your serving glass half full with ice, then add the grapefruit juice. Strain in the drink on top of the juice gently. Top the drink off with sparkling water, and add a slice of grapefruit for garnish if desired.
Give the drink a good stir before enjoying!
Recipe Notes
I used gin infused with butterfly pea tea flowers, but a more traditional clear gin is fine here too.