This dish shows how the lowly onion can be transformed into a succulent sauce by slow, lengthy cooking and the addition of capers and a few, almost undetectable, anchovies.
Put the olive oil and anchovies in a 12-inch skillet and place over medium low heat. Cook, stirring, until the anchovies have dissolved. Add the onions, season with salt and pepper (go light on the salt because of the anchovies), and continue cooking until the onions have wilted