Melt the butter in a soup pot. Add the onions and wilt over medium low heat, covered, for 20 minutes, stirring occasionally.
Sprinkle the sugar over the onions, toss, and cook, uncovered, until caramelized, 10 minutes. Sprinkle with salt and pepper
Add 3 cups of the stock and simmer, uncovered over medium heat for 15 minutes. Then add the remaining 3 cups of stock and the wine; cook until the broth is rich in taste, another 30-40 minutes
Preheat the broiler, or the oven to 350
Divide the soup among four ovenproof bowls. Top each with a slice of toasted French bread (I like to tear mine in bite size pieces) and sprinkle the cheese evenly on top. Place under the broiler until the cheese melts or back until the cheese melts and the soup is bubbly.