In a soup kettle over medium low heat, cook onions, sugar, and pepper in oil for 20 minutes or until onions are caramelized, stirring frequently. Add the broth, bring to a boil. Reduce heat; cover and simmer for 30 minutes. Ladle soup into ovenproof bowls. Top each with a slice of toasted French bread; sprinkle with cheese. Broil until cheeese is melted. Serve immediately.