Fizzy Rosemary Cider Mocktail

To prepare simple syrup: Combine water, sugar substitute, and rosemary in a small saucepan. Cook, stirring, over medium heat until the sugar substitute is completely dissolved, about 1 minute. Remove from heat and let cool for 30 minutes. Remove and discard the rosemary sprig. 

To prepare mocktail: Combine cider, club soda (or seltzer) and simple syrup in a highball glass. (Reserve remaining simple syrup for another use.) Garnish with rosemary sprig, if desired.