Combine demerara sugar and water in a small saucepan over medium heat. Stir until the sugar has fully dissolved.
(Optional) For an added smoky flavor, lightly torch the rosemary sprigs to release their aroma.
Add the rosemary sprigs to the syrup, then remove the saucepan from heat.
Let the rosemary steep for about 2 hours, allowing the syrup to infuse with herbal flavor.
Remove the rosemary sprigs and let the syrup cool to room temperature.
Transfer to a container and refrigerate.
Notes
The semi-rich syrup ratio (1.5 parts sugar to 1 part water) creates a thicker, more flavorful syrup perfect for cocktails.Adjust steeping time or number of rosemary sprigs to control the intensity of rosemary flavor.Light torching the rosemary adds a unique smoky note that complements whiskey or other smoky cocktails beautifully.