Halve the red onion from top to bottom, cutting down through the stem. Place the flat sides down on the cutting board.
Slice each half VERY thinly (as thin as you can) lengthwise (that’s through the stem, the same direction you cut it initially). Transfer to a 1 1/2 pint (24 ounce or 3-cup) or larger mason jar (I use these jars and a medium red onion fits just right) or a similar heat-proof storage container.
In a medium saucepan, heat the water, white vinegar, apple cider vinegar, honey, kosher salt, and any additional spices over medium-high, just until the mixture comes to a simmer. Whisk together the ingredients until the honey dissolves.
Place the onion jar in the sink to catch any splashes, then pour the warm pickling liquid over the top (including any whole spices). Use a dull knife or small spoon to lightly stir and push the onions around and down. Ensure the onions and spices are submerged. Let sit for at least 15 minutes prior to use (30 minutes is even better). Or, cool to room temperature, cover, and refrigerate for up to 3 weeks.
These pickled onions CANNOT be canned. It was developed for pickles that are stored in the refrigerator only. If you’d like to can them, please use a different recipe designed specifically for canning, as this one is not safe to can. (I don’t have a particular recipe I recommend, but a quick online search should turn up some great options.)
TO STORE: Pickled onions can last in the refrigerator for up to 3 weeks. I like them best during the first week because they are the most crisp, but they’re still yummy later on.
Nutrition facts have been calculated without the pickling liquid (for the onion only), as the liquid is discarded. Please note, nutrition facts are a general guide only. For a more specialized calculation, you can play around with the recipe amounts at no charge at websites such as myfitnesspal.com