Melt butter in a large Dutch oven over medium heat. Add onion to pan; cook 5 minutes, stirring occasionally. Partially cover, reduce heat to medium-low, and cook 15 minutes, stirring occasionally. Add sugar and pepper; cook, uncovered, until deep golden brown (about 35 minutes), stirring frequently. Sprinkle onion with flour; cook 2 minutes, stirring constantly. Add broth, water, and wine; bring to a boil. Reduce heat, and simmer 30 minutes. Add Worcestershire sauce; stir well.
Preheat broiler to high.
Arrange bread slices in a single layer on a jelly-roll pan; broil for 2 minutes or until toasted, turning after 1 minute.
Divide soup evenly among each of 4 broiler-safe soup bowls. Top each serving with 1 bread slice and 1 cheese slice. Place soup bowls on jelly-roll pan; broil for 4 minutes or until tops are golden brown and cheese bubbles.
This recipe was updated for the November, 2012 25th anniversary issue.