Roll the rosemary sprig with your palm to express the oils, then rub it around the inside of a glass. In a mixing glass, stir all of the ingredients with ice, then strain into the prepared glass, adding the sprig as garnish.
Rosemary Syrup: Combine 1 cup each of water and granulated sugar in a small saucepan over medium heat, and stir until sugar has dissolved. Add 2 to 3 sprigs of fresh rosemary, and once the mixture comes to a boil, remove it from the heat and let the syrup come to room temperature. Strain out the solids, then bottle for use; keeps refrigerated for up to 1 month.