First melt butter in a large pot over medium heat, add the onions and cook until onions are caramelized about 25 minutes. When onions are done, add garlic, bay leaves, thyme, salt and pepper until they combine nicely about a few minutes. Next add the mushrooms and wine, then bring to a boil. Reduce heat and simmer until the wine has evaporated. Next add the beef broth and cook for 15 minutes. Season, to taste, with salt and pepper.