In a small saucepan, combine the sugar, water, and a few leaves of fresh sage. Bring to a simmer, pressing on the sage with the back of a spoon to release the oils. After a couple of minutes, remove from heat and let cool completely.
To make the greyhounds, combine the grapefruit juice, vodka, and sage simple syrup in a cocktail shaker. Fill with ice, and shake until the outside starts to get frosty, about 20-30 seconds. Strain into two martini glasses. Twist a sage leaf over each cocktail to release the oils. Garnish the cocktail with fresh sage. Serve!
I took the easy way and used some high-quality grapefruit juice from the grocery store. However, if you would prefer to do fresh, plan on juicing about one or two large grapefruits!Other herbs, like rosemary or thyme, would be delicious in place of sage.