It's easy to make with the recipe I found at allrecipes.com.
Below are my alterations to the above link. Though I like to start with the original recipe, I didn't have everything on hand this time. Do check out the original recipe! It has additional goodies (and unsalted butter) that would make it better, I'm sure!
In a stock pot, brown onions in butter and oil, stirring frequently. Add broth, thyme, salt, and pepper to taste. Bring to boil and simmer for 30-45 minutes.
Ladle soup into oven safe bowls. Add cheese and bread, layering. (If you have broiler-safe bowls, good for you and use your broiler. I did not.) Bake at 400 for 5-10 minutes until cheese on top is melted and slightly browned.