Add rosemary along with sugar and 1 cup water to a small saucepan. Bring to simmer and stir until sugar dissolves. Turn off heat and allow it to steep for 30 minutes until it cools. Remove rosemary and store in an airtight jar in refrigerator.
In a mixing glass three-quarters filled with ice, combine all liquid ingredients. Stir until chilled, about 30 seconds. Strain into a chilled coupe glass. Garnish with a small slice of grapefruit or rosemary sprig.
