01 - In a medium saucepan, combine root beer, ketchup, brown sugar, Worcestershire sauce, apple cider vinegar, and butter. Bring to a simmer over medium heat, stirring until sugar dissolves and butter melts.
02 - In a small bowl, mix cornstarch and water to create a slurry. Whisk the slurry into the simmering glaze. Cook, stirring frequently, until the mixture thickens and becomes glossy, approximately 3–5 minutes.
03 - Add the cooked meatballs to the saucepan. Gently toss to ensure they are evenly coated with the glaze. Simmer for 5–7 minutes, turning occasionally, until the glaze clings to the meatballs and they are heated through.
04 - Transfer the glazed meatballs to a serving platter. Garnish with halved maraschino cherries and chopped parsley, if desired. Serve warm with cocktail picks.