In a small saucepan, bring sugar, ¾ cup water, and rosemary to a boil over medium heat. Cook, stirring occasionally, until sugar is dissolved, about 5 minutes. Remove from heat; let stand for 15 minutes. Strain, discarding rosemary. Refrigerate until ready to use.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/rosemary-bourbon-sour-recipe/