How to Make It
Toss together 8 red plums, chopped, 3/4 cup granulated sugar, 3/4 cup packed light brown sugar, 2 fresh culinary lavender sprigs, and 1 vanilla bean, split, in a medium bowl. Cover tightly, and let stand at room temperature 2 days.
Discard lavender sprigs and vanilla bean, and stir in 1 1/2 cups apple cider vinegar. Cover and chill 24 hours. Pour mixture through a fine wire-mesh strainer into a small pitcher, discarding fruit.
For each serving, pour 1/4 cup of the syrup over ice in a 12-ounce glass and stir in 3 tablespoons bourbon or rye whiskey. Top each with 1/2 cup club soda. Garnish with lavender sprigs and plum slices.