Nigel Slater very usefully points out that if you soak onions in vinegar and salt before putting them in a salad, they become mellow.
Even better, if you don’t need to use the whole onion in a salad for two, you can leave the remains in the vinegar, in the fridge, and it will keep for at least a week.
And it will become tastier and tastier and tastier.
Red onions, red wine vinegar and a tiny sprinkle of sea salt.
I wonder if I make a whole jar, with some molasses and mustard seeds as well?