Prepare the caramelized onions as directed in a slow cooker first. When onions are ready, bring to a boil the beef broth, chicken broth, sherry, Worcestershire sauce, garlic, thyme and the caramelized onions. Allow to simmer for several minutes to cook the garlic and to marry the flavors. Divide the hot soup mixture into four oven proof crocks or cups that you have placed on a sturdy cookie sheet. (A flimsy cookie sheet may warp and spill during broiling process.)  Add the croutons to each crock and top with the slices of cheese. Sprinkle each crock with Parmesan cheese. Preheat the broiler on HIgh and place the oven rack about 6 inches from the heating element. Place under the broiler for approximately ONE minute, or until the cheese is bubbling and beginning to brown. WATCH CAREFULLY. Remove the cookie sheet with potholders and serve immediately.