Add plums, sugar, water and spices to a small pan and bring to a boil, gently crushing the plums with a wooden spoon.
Add the Olivia’s Cranberry Pear Balsamic and let simmer for 3-4 minutes on medium-low and then remove from heat. Let sit for 15 minutes, then strain syrup through a fine mesh sieve, pressing down gently on plums.
Refrigerate plum syrup for up to 10 days. Save reserved plums for ice cream or yogurt if desired, and discard spices and rosemary.
Pour 1 oz. plum syrup into 4 glasses filled with ice and top up with 1 oz. soda water. Stir together then top up glasses with Prosecco, a small sprig of rosemary and plum slices.
