Spicy Pickled Fiddleheads

Ingredients

• 1
  pound fiddlehead ostrich ferns
• 1
  medium onion, quartered, cut into thin slices
• For the Brine:
• 1
  cup water
• 1 ¼
  cups white-wine vinegar, or apple cider vinegar
• ¼
  cup honey
• 1
  tablespoon kosher salt, or another non-iodized salt
• 1
  or 2 small fresh or dried hot chile peppers, chopped or crushed
• ½
  teaspoon whole mustard seeds
• ½
  teaspoon whole coriander seeds
• ¼
  teaspoon whole cumin seeds
• 6
  to 8 whole black peppercorns
• 4
  to 6 whole spicebush berries, or allspice berries