Cate's Pickled Red Onions

Pack a wide-mouthed jar with thinly sliced red onions, leaving a 1/2 to 1-inch space between the onions and the top of the jar.

In a saucepan, combine apple cider vinegar and sugar and bring to a boil, stirring constantly until sugar melts; pour over onions, covering completely.

Let cool and regrigerate up to 3 weeks.

***TO ADD SOME SPICE: add 1/2 cinnamon stick or a few few cloves, fresh ginger slices, allspice berries, garlic cloves, mustard seeds, or cumin seeds to the vinegar and sugar before boiling. Remove the spices after the onions cool, before refrigerating.