Make the simple syrup
1
Combine one cup sugar, one cup water and two large sprigs of fresh rosemary in a saucepan. Simmer until the sugar has dissolved. Cool and discard the rosemary.
Pour into a shaker
2
Combine two ounces of gin, three ounces ruby red grapefruit juice and one ounce rosemary simple syrup into a cocktail shaker full of ice.