Place half the onions in a single layer in a wide, fairly shallow flameproof casserole dish, half in another, similar casserole dish.

Sprinkle both with a little salt and add 5 fl oz (150 ml) water, 7fl oz (200 ml) vinegar and a piece of orange rind to both batches.

Heat to boiling point, cover and cook over a low heat for 10 minutes.

Sprinkle half the sugar over each batch of onions, stir, replace the lids and simmer very gently for 10 minutes more or until the liquid has almost completely evaporated and the surface of the onions is glazed and glossy.