Make the simple syrup: Add water and sugar to sauce pan, cook, stirring frequently, over medium high heat until sugar has dissolved and mixture thickens a bit. Remove from heat and add rosemary sprig. Set aside to cool.
After mixture has cooled, remove rosemary sprig.
Add simple syrup to blood orange juice. Cool in refrigerator for 30 minutes to 1 hour.
Add the cooled mixture to your ice cream machine. If you’d like to add the liquor, do so now. Follow you ice cream maker’s directions for times- usually 20 to 30 minutes. Freeze at least 1 hour before serving.