Melt butter in medium saucepan over medium heat and cook Recipe Ready Chopped Onions, stirring occasionally, 15 minutes or until golden brown.
Add beef broth and thyme; bring to a boil over high heat. Simmer 5 minutes. Season, if desired, with salt and black pepper.
Arrange 4 oven-proof soup bowls on baking sheet and evenly fill with soup. Arrange toast in each bowl and top with cheese. Broil 1 minute or until cheese is bubbling.