Melt butter in a Large soup pot on Medium heat. Add olive oil and stir in onions. Cook until onions are clear, but not brown.
Add beef broth, thyme, salt, pepper. Simmer for 30 minutes. Meanwhile, toast bread in the oven until golden brown.
Pour soup into individual oven-safe bowls. Place one slice of tasted bread on top of the bowl, add 1 slice of provolone, the shredded swiss cheese, and parmesan. Broil in oven until the cheese is bubbly.