Vinegary Red Onions - remember these?

Remember a couple of weeks ago when I wrote up the Stacked Enchiladas? They had these crispy, crunchy onions as a garnish with drizzled Mexican crema? (You can read the full recipe on my May 2nd post, otherwise just the onions are below.) Well, the Stacked Enchiladas are long gone, but I'd put the remains of these onions in a little plastic baggie in the refrigerator. You know how sometimes you poke around in there and find all kinds of gems? Maybe moldy gems. Perhaps something unidentifiable? And then, perhaps some tasty gems when you're trying to throw together something in a hurry, and it doesn't LOOK like there's anything in the darned thing? This was lunch yesterday - Dave and I shared this one sandwich. It was some wonderful Citterio rosemary ham from Trader Joe's, a little smear of Best Foods mayo, some pale ale mustard, sliced vine-ripened tomatoes, a few thin slices of avocado, a good grinding of freshly ground black pepper, and then I topped it with the vinegary red onions and some feathery leaf lettuce. Lo and behold - a magnificent sandwich. It's the crunch that is the lure for me. I'll make these again just for other dishes. I used some of the onions in a tuna salad sandwich a week or so ago, which were also delicious, and still had some left. These aren't nibbling onions - they're far too sour, vinegar-y (just like they're supposed to be) but laced on a sandwich they're sensational. Here's a repeat of just the onions:

Vinegary Red Onions

1 whole red onion, peeled, thinly sliced

3/4 cup rice wine vinegar

Place onions in a medium skillet. Add vinegar and bring to a boil over high heat, stirring occasionally, about 2-3 minutes. Remove from heat and let stand until cool, stirring often. Add salt to taste. Serve immediately, or cover and refrigerate up to 3 days. Serve with a slotted spoon. Note: obviously these keep far longer than 3 days. It's been 2 weeks and counting.