• Melt butter in a wide-bottomed soup pot set over medium heat and add sliced onions, sugar, and salt. Slowly caramelize onions over 30 minutes, stirring occasionally. Onions are done caramelizing when they are sticky and turn a deep brown color.
• Add minced garlic to the onion mixture and cook an additional two minutes or until fragrant. Then sprinkle in the flour, stirring to incorporate it evenly. Cook the flour for two minutes while stirring continuously to prevent scorching.
• Deglaze the pot with the white wine by stirring it into the mixture then scraping the brown bits off the bottom of the pot, letting it incorporate into the liquid.
• Stir in the beef stock, Worcestershire sauce, fresh thyme sprig, bay leaves, and fresh ground pepper. Bring soup to a simmer for ten minutes, then add heavy cream and simmer for 5 additional minutes.

Serving

• Ladle soup into oven-safe ramekins and top with a slice of toasted French bread, then top generously with grated cheese. Place under the broiler until cheese is melted and bubbling, then serve immediately.