Heat oil in a large nonstick skillet over moderate heat. Add onions and cook, stirring, until golden brown and tender, about 5 minutes.

Stir together sugar, vinegar, bay leaf, and cranberries in a large saucepan. Simmer, stirring occasionally, until cranberries begin to pop, about 10 minutes. Remove and discard bay leaf; salt and pepper to taste. Stir in onions and transfer to a bowl to cool. Chill, loosely covered, until cold, about 1 hour. Makes 8 servings.