In a large dutch oven over medium-low heat, add butter, olive oil, and sliced onions. Stir to coat onions in butter then allow to cook untouched for 10 minutes, until caramelizing begins. Stir well, then allow to cook for an additional 5 minutes untouched. Stir, cook another 5 minutes, onions should be turning a nice golden brown. Continue cooking, stirring every 3-4 minutes until the desired color is achieved.
Add in minced garlic, bay leaf, fresh thyme, salt, and pepper. Cook for an additional minute, then add in wine and Worcestershire sauce. Allow to simmer gently until the wine has absorbed. Remove bay leaf and thyme sprigs, discard.
Dust onion mixture with flour and cook slowly for 5-7 minutes. Then add beef broth and simmer 10 minutes.
Preheat oven to broil. Butter and toast crusty bread slices. Ladle soup into crocks, place toasted bread on top of each crock and top with a slice of cheese. Broil until lightly browned and bubbly.