2 red onions, halved vertically and then sliced 1.5 cups apple cider vinegar 1 Tbsp brown sugar 1 Tbsp pickling spice 1 tsp red pepper flakes 1 garlic clove 1.5 tsp salt. 0.5 cup water Pack 4 cup jar with onions (or two smaller jars) Mix other ingredients and bring to a boil. Allow to cool for 5 minutes, then pour over onions. Add lid and refrigerate for at least 24 hours before eating.