Pickled Red Onions From 'The Artisan Jewish Deli at Home'

Combine onion, vinegar, sugar, bay leaves, cinnamon stick, crushed red pepper, if using, peppercorns, cloves, and salt in a medium saucepan. Bring to a boil over high heat, stirring to dissolve sugar. Boil for 1 minute. Add onions and then remove pan from heat. Allow onions and pickling brine to cool to room temperature, and then transfer to a nonreactive container with a tight-fitting lid. Refrigerate for 1 day to allow flavors to meld. Pickled red onions will keep in refrigerator for up to 1 month.