In a large pot, gently sauté the onions in the butter until they caramelize, about 15 minutes. Season with salt and pepper. Deglaze with the wine. Add the broth and tomatoes. Bring to a boil and simmer for about 10 minutes. Season with salt and pepper.
With the rack in the middle position, preheat the oven’s broiler.
Ladle the soup into ovenproof bowls or baking dishes. Top with the bread slices and sprinkle with the cheese. Brown in the oven.
Sweet onions are usually identified as such in the grocery store. We used varieties of red or Vidalia onions but you can, of course, use any other kind of onions.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.