Follow this simple recipe to turn cauliflower into a deliciously creepy Halloween hors d'oeuvre. Martha displayed this spook-tacular appetizer on a specialMonster Buffet during her Halloween Monster Bash with Jimmy Fallon.
Place cauliflower in a large glass heatproof jar or canister, positioning florets against the glass; set aside.
Fill a large pot with 8 cups water. Add both vinegars, sugar, salt, peppercorns, mustard seeds, and onions. Bring to a boil.
Carefully pour boiling liquid over cauliflower; let cool to room temperature. Cover and transfer to refrigerator. Let chill overnight or up to 1 week.