It's accepted knowledge here in the Test Kitchen that the easiest (and most appropriately-named) recipe in the world is simple syrup. Equal parts sugar and water brought to a boil. Simple, huh?
And guess what? Add an equal amount of vinegar to the mix, and voilà: a quick pickling solution!! Pour the hot liquid over some very thinly sliced onions and chill them for several hours or overnight. They give sandwiches, salads, or grilled meats a sweet and sour spike.
I used red wine vinegar to give red onions an additional visual punch. But you can use white or yellow onions and white wine or cider vinegar works just as well. You can add a pinch of salt if you want or some additional spices, but really you don't have to get too fancy here.
Here they add a peppy touch to a grilled radicchio and peach salad.