Step 1

Place a fine mesh strainer over a medium-size sauce pot. Squeeze grapefruit juice over the strainer to catch any seeds or pulp.

Step 2

Add sugar and stir. Heat mixture on medium high until sugar dissolves then increase heat to high until mixture begins to boil. Allow the mixture to simmer for 5-7 minutes it will thicken slightly. Allow to cool and then transfer to a heat safe pitcher and refrigerate until well-chilled.

Step 3

To prepare the cocktail, fill a champagne flute with 2 tablespoon of the grapefruit syrup fill ¾ of the way full with the rosé then add a triangle of sliced grapefruit and a sprig of rosemary.