In a large non-stick saucepan, heat 1/4 cup vegetable broth. Stir in the onion and cook over medium heat until golden, 15 minutes. Stir in the sugar and flour. Pour in the remaining 5 cups vegetable broth and the wine. Stir in the bay leaf, thyme and black pepper. Bring to a boil and let boil 8 minutes, stirring constantly; then reduce heat, partly cover, and simmer 30 minutes. Preheat oven broiler. Remove from heat, remove bay leaf and stir in brandy. Rub garlic clove over toast. Ladle the soup into 4 ovenproof bowls and float a piece of toast on top of each bowl. Sprinkle with the Parmesan. Place bowls under broiler until cheese melts.