In a Dutch oven, saute onions and thyme in 1 tablespoon butter until onions are tender, about 8 minutes. Reduce heat; cook, uncovered, over low heat for 20 minutes or until onions are golden brown, stirring occasionally. Remove onions to a bowl.
In the same pan, melt remaining butter. Add mushrooms, brandy if desired and garlic; saute for 1 minute. Return onions to pan. Add broth, wine and pepper; bring to a boil. Reduce heat; cover and simmer for 40-45 minutes or until onions are very tender.
Meanwhile, place French bread slices on a baking sheet; top each slice with provolone cheese. Broil 4-6 inches from the heat for 1-2 minutes or until cheese is melted. Discard thyme sprigs from soup; top soup with cheese-topped bread.