1. Preheat oven to 450 degrees F.
2. In a large roasting pan, toss leeks, Vidalia onions, red onions, garlic, oil, salt, pepper, and thyme until well mixed. Place on middle rack and roast for 30 minutes.
3. Remove from oven, add wine, and stir well. Roast another 15 minutes.
4. Remove from oven and transfer onions to a large pot. Use 1/2 cup broth to scrape up any bits clinging to bottom of roasting pan. Add this and remaining broth to pot with onions.
5. Simmer soup, partially covered, for 30 minutes. Taste for seasoning.
6. Meanwhile, preheat broiler. Place baguette slices on a baking sheet. Broil 1 minute or until just barely toasted. Remove and flip slices over. Sprinkle 1 Tbsp. cheese on top of each slice and broil another 1 to 2 minutes, or until cheese is melted and bubbling. Remove from oven and keep in a cool, dry place until ready to serve. (Croutes can be made a day ahead of time.)
7. Serve hot, each bowl topped with 1 or 2 croutes and a sprinkling of parsley.
Source: Hannaford fresh Magazine, January - February 2008