balsamic-glazed sweet and sour cipollini

INGREDIENTS

• 2 pounds cipollini or small (1 1/2-inch) onions
• 4 tablespoons virgin olive oil
• 3 tablespoons sweet butter
• 2 tablespoons sugar
• 1 cup balsamic vinegar
• 1/2 cup tomato sauce of your choice (I cheated and used canned. Don’t tell!)
• 1 cup water
• 1 teaspoon chopped fresh rosemary leaves