Working in 2 batches, blanch
the onions in a medium pot of boiling water for 3 minutes. Peel
Heat the oil over medium heat in a large skillet. Cook, turning the onions over as they brown, until almost tender, about 15 minutes. Add the broth, vinegar, sugar and raisins
and bring to a boil. Reduce to a simmer
and cook until the sauce
is slightly thickened and the onions
are tender, 3 to 5 minutes. Stir in the salt and serve.