Preparation

• Peel and thinly slice the onions from root to stem. There should be about 10 cups of sliced onions in total.
• In a 5 to 6 quart thick-bottomed pot, heat 3 tablespoons of olive oil on medium heat. Add the onions and toss to coat with the olive oil. Cook the onions, stirring often, until they have softened, about 15 to 20 minutes.
• Increase the heat to medium high. Add the remaining tablespoon of olive oil and the butter and cook, stirring often, until the onions start to brown, about 20 to 40 minutes.
• Sprinkle with sugar and 1 teaspoon of salt. Continue to cook until the onions are well browned, about 10 to 15 more minutes. Add the minced garlic and cook for a minute more.
• Add the wine or vermouth to the pot and scrape up the browned bits on the bottom and sides of the pot.
• Add the stock, bay leaves, and thyme. Bring to a simmer, cover the pot and lower the heat to maintain a low simmer. Cook for about 30 minutes.
• Season to taste with more salt and add freshly ground black pepper. Discard the bay leaves. Add brandy if using.
• While the soup is simmering, line a sheet pan with parchment paper or foil and preheat the oven to 450°F. Brush both sides of the French bread slices lightly with olive oil. Toast the bread until lightly browned, about 5 to 7 minutes. Remove from oven and sprinkle with the grated Gruyere cheese and Parmesan.
• To serve, ladle soup into a bowl and transfer one cheesy toast onto the top of each bowl of soup. Optionally, use individual oven-proof bowls or one large casserole dish and cover with the toast and sprinkle with cheese. Broil for 10 minutes at 350°F until the cheese bubbles and is slightly browned.