Cook onion in hot oil in a Dutch oven over medium-high heat, stirring occasionally, 45 minutes or until onion is caramel colored. Add garlic, and cook 1 minute. Stir in 8 cups water. Bring to a boil; stir in bouillon granules, pepper, thyme, and, if desired, sherry. Cover, reduce heat, and simmer, stirring occasionally, 20 minutes.
Ladle soup into individual bowls, and top with Goat Cheese-and-Chive Croutons. Garnish, if desired.
