In a saucepan of boiling water blanch one third of onions 3 minutes and drain. Blanch remaining onions in batches in same manner. Cool onions and peel.

In a large heavy skillet heat oil over moderately high heat until hot but not smoking and saute onions until lightly browned, about 5 minutes. Add vinegar and water and simmer, stirring occasionally, until onions are tender, about 15 minutes. Transfer onions with a slotted spoon to a platter, reserving liquid. Glazed onions may be prepared up to this point 2 days ahead and onions and reserved liquid chilled separately, covered. Reheat onions in reserved liquid, adding a little water if necessary, and transfer with slotted spoon to platter. Simmer reserved liquid until thickened and syrupy and reduced to about 1/2 cup.

Spoon sauce over onions and serve warm or at room temperature.