I stumbled upon a recipe from Food in Jars about pickled red onions. I'm not a fan of onions unless they are slices super thin or diced fine- otherwise they're just big bites of pungent flavor that I don't enjoy. I took a chance with this recipe and and am so happy I did. The result is a sour and sweet thin onion that is perfect on sandwiches or burgers. I highly recommend it, and it takes little or no time to make.
3 pounds of thinly sliced red onion (I used my food processor to slice them)
2 cups apple cider vinegar (I used a local vinegar- make sure it has at least 5% acidity)
1/2 cup cold water
3/4 cup white sugar
1 tbsp pickling salt
2 tsp mustard seed
1 tsp celery seed
1/2 tsp red chili flakes
1) Combine water, vinegar, salt, sugar in a pot and bring to a boil.
2) Then, turn down stove to medium heat and add onions. Stir onions and watch for them to soften, it took me about 5-6 minutes.
3) Sterilize jars and simmer lids.
4) In sterilized warm jars, add an even amount of spice in each jar. Then, fill with onion and brine mixture, leaving 1/2" headspace.
5) Remove air bubbles from jars, wipe rims, then affix lids and screwbands. Process in hot water bath for 10 minutes.
6) Test lids to make sure they've set after they've cooled. If they didn't set, you can store them in the fridge.