Saute onions in butter over medium heat 15 minutes, stirring frequently. If desired, sprinkle with sugar. Caramelize approximately 45 minutes. Season with salt and pepper. Add half the broth; simmer uncovered 15 minutes. Add remaining broth; simmer another 25 minutes. Add wild rice; simmer 5 minutes, remove from heat and stir in wine. Top each serving with 3 bread slices; sprinkle with cheese. Broil to melt cheese. Serve immediately.
