Method:

• Peel and cut the onions into slices to measure 4 cups. In a 4-quart nonstick Dutch oven, melt the butter over medium-high heat. Stir in onions to coat with butter. Cook uncovered 10 minutes, stirring every 3 to 4 minutes.
• Reduce heat to medium-low. Cook uncovered 35 to 40 minutes longer, stirring well every 5 minutes, until onions are deep golden brown (onions will shrink during cooking).
• Stir in broth, water, pepper, thyme and bay leaf. Heat to boiling over high heat. Once mixture is boiling, reduce heat just enough so mixture bubbles gently. Cover with lid; simmer 15 minutes.
• You may need to move the oven rack so it is near the broiler. Set the oven control to broil. On a cookie sheet, place the bread slices. Broil with tops about 5 inches from heat 1 to 2 minutes or until golden brown. Turn bread over; broil 1 to 2 minutes longer until golden brown. Place toasted bread in 4 ovenproof bowls or individual ceramic casseroles (do not use glass, which cannot withstand heat of broiler and may break).
• Remove bay leaf from soup. Ladle soup into bowls. Top with shredded Gruyère cheese. Sprinkle with Parmesan cheese. Place bowls in pan with shallow sides.
• Broil soup bowls with tops about 5 inches from heat 1 to 2 minutes or just until cheese is melted and golden brown. Watch carefully so cheese does not burn. Serve with additional French bread if desired.