Plum Cocktail by Saugatuck Grain & Grape for Sept's FIO

The recipe for the plum cocktail:
2 oz Vodka
3/4 oz St. Germain
3/4 oz plum & rosemary syrup  (recipe below)
1/5 oz lemon juice
Shake and pour into a rocks glass and top with a little club soda
Plum & rosemary syrup:
2 cups water
1 cup sugar
18 plums, peeled and chopped
4 sprigs rosemary.
Bring the entire thing to a slow boil and then reduce it to a simmer until the plums have cooked down to a syrup. Stir somewhere between “constantly” and “often” because you don’t want to burn it. Remove the rosemary before you pour the syrup into a jar.