Add yellow and red onions, sugar, red wine and garlic and cook until onions are softened.
Reduce heat to low and cook mixture for 20 to 25 minutes, until onions are golden and wine is absorbed.
Add broth, scallions, salt and pepper; heat eat for 3 or 4 minutes.
Pre-heat broiler.
Ladle soup into oven proof bowls.
Place a slice of French bread on each soup serving.
Top bread with shredded cheese.
Broil about 5 minutes or until cheese is light brown and bubbly.
Serve immediately.
Notes
Sometimes, I use Swiss cheese instead of Gruyere and toast the French bread, ahead of time, before placing the cheese on the bread and placing in broiler for 5 minutes.