Combine sugar, water, and cinnamon sticks in a small saucepan over medium heat. Bring to a simmer, stirring occasionally, until sugar is dissolved. Remove from heat and let sit at room temperature overnight.
Remove cinnamon sticks and store syrup in an airtight container in the fridge for up to two weeks.
Recipe adapted from: Kaplan, David, Nick Fauchald, and Alex Day. “Cobra's Fang.” Death & Co. Modern Classic Cocktails. Berkeley: Ten Speed Press, 2014.