What’s a shrub? Think of it as a vinegar-based fruit syrup that can be used in myriad ways: as a cocktail mixer, as a refreshing cooler with sparkling water, or as a juice concentrate to ramp up the flavor of many dishes. This drink is hundreds of years old and has recently become popular again. Brought from England by colonists, shrubs have a rich history in American cooking. This blueberry shrub recipe is the definition of seriously simple. My dear friend and colleague Cynthia Graubart penned “Blueberry Love,” an homage to the versatile berry that you might find in a cooling soup, sauce for chicken, many desserts, and the following recipe. Summer appears to be hanging on, so why not take a break and enjoy this refreshing beverage when it’s just too hot to do much? In these dog days of summer, try this delectable shrub with your favorite alcohol …