1. In 4-cup glass measure, combine butter and onions. Microwave, uncovered, on high 1 minute or until onions are wilted.
2. Stir in soup, water and vermouth. Microwave, uncovered, on high 5 minutes or until boiling, stirring once during cooking.
3. Ladle soup into four 10-ounce bowls. Sprinkle croutons over soup; sprinkle with cheese. Let stand, uncovered, 1 minute or until cheese is melted.