Much like pickles, onions are usually thought of as a sandwich topping rather than the “meat” of the dish. But (also like pickles) onions can be the star of the sandwich show—if you take a little time to prepare them correctly.
Thick slices of raw onion are obviously not the way to go. Big rings of cold onion between two slices of bread would not taste very good, and could (potentially) upset your stomach a bit (and give you terrible breath). If you’re going to use this powerful ingredient as a primary sandwich filling, you either need to slice it very thin, or cook it very gently.
If you want to cook ‘em gently
This particular sandwich (the one in the photo above) comes to us via my favorite TikToker, Mr. Kevin Ashton of pickle cheese crisp fame.
It’s a savory, sweet, caramelized delight with few ingredients but a ton of developed flavor. The sauce is made with a whole head of roasted garlic, mayo, Dijon, and lemon, and the onions are gently cooked in a mixture of olive oil and butter over low heat until the they soften and caramelize. Everything is loaded onto some toasted sourdough, and the result is a surprisingly mellow sandwich.
You could of course add some cheese or some accent bacon, make your own sauce, or add whatever toppings you think would go well with a melty mass of softened, caramelized onions, but I urge you to try Ashton’s version first, as it is delightful in its simplicity.
If you want to slice ‘em thinly
Food historians and enthusiasts might recognize this little tea sandwich, a James Beard original that is somehow delicate, sweet, and creamy, even though it’s little more than white onions, mayo, and salt on brioche (with a border of fresh parsley).
You can see the exact ratios recommended here, but if you want to make just a few of these babies at a time, you’ll need a quarter of a small white onion to make three tea sandwiches (scale up or down as you desire).
For the bread, you’ll want something soft, squishy, and kind of sweet, like challah or brioche. Cut the bread into thin slices and cut out rounds with cookie cutters, or grab some slider buns and trim off the tops and bottoms with a bread knife. Slice the onions as thinly as you can with a sharp knife—you want them to be nearly translucent—then spread each bottom piece of bread with a thin layer of mayo. Equally divide the onions between the sandwiches and pile them on top of the mayo, then sprinkle each pile with a generous pinch of salt. (Do not skip the salt, it is what softens and tames the onion.)
Close the sandwiches, then brush the edges with a little more mayo and roll them in chopped parsley. Chill in the fridge for an hour, then serve. (Do not leave overnight, as the bottoms will get soggy and the tops will dry out.)