Green beans with caramelized onions

• 2 pounds green beans, stem ends snipped off
• 2 tablespoons butter
• 2 medium onions, sliced as thinly as possible
• 1 cup chicken stock
• 1/2 tablespoons sugar
• 1 tablespoon red wine vinegar
• salt and pepper to taste

Cook beans in boiling salted water until crisp-tender, 2-4 minutes. Drain; immerse in ice water. Drain again and let stand to dry. Melt butter in skillet over medium flame. Stir in onions and cook them slowly until very wilted and deepened in color, about 15 minutes. Boil stock in a saucepan until reduced to 1/4 cup; stir in sugar and vinegar. Stir in onions. Simmer until slightly reduced. Combine onions and green beans; heat through. Season with salt and pepper. Makes 8 servings.