Ingredients
Method
Whisk apple cider vinegar, red wine vinegar, rice vinegar, white wine vinegar, sugar, salt, peppercorns, coriander seeds, juniper berries, red pepper flakes, garlic, bay leaf, and 1¼ cups water in a medium bowl until salt and sugar dissolve. Pour brine into an airtight nonreactive container and add onions. Cover and chill at least 1 week. Flavors will deepen the longer the onions sit; the liquid starts getting really delicious after 1 month.
Do Ahead: Pickled onions can be made 3 months ahead. Keep chilled.
For each cocktail, pour 2 oz. gin, ½ oz. blanc vermouth, ½ oz. dry vermouth, and ¼ oz. onion pickling liquid over 4 cups ice in a large measuring or stirring glass and stir 1 minute. (Yes, a full minute. This dilution is key to rounding out the flavors of the finished drink.) Strain into a martini glass and garnish with a pickled onion.
