(Serves 4 with leftovers)
6 large red or yellow onions (about 3 pounds), peeled and thinly sliced
4 tablespoons olive oil
2 sticks of butter
2 cloves garlic, minced
8 cups beef stock
2 bay leaves
1 teaspoon thyme
1/2 teaspoon freshly ground black pepper
8 slices (1 inch thick) French bread or baguette
1 1/2 cups grated Gruyere
Sprinkling of Parmesan
1. Caramelize the onions 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 15 more minutes.
2. Sprinkle 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.
3. Add the stock, bay leaves, and thyme and 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.
4. While the soup is simmering, line a sheet pan with parchment paper and preheat the oven to 450°F with a rack in the upper third of the oven. Brush both sides of the French bread or baguette slices lightly with olive oil
5. Put in the oven and toast until lightly browned, about 5 to 7 minutes. Remove from the oven. Turn the toasts over and sprinkle with the grated Gruyere cheese and Parmesan. Return to the oven when it's close to serving time and bake until the cheese is bubbly and lightly browned.
6. To serve, ladle soup into a bowl and transfer one cheesy toast onto the top of each bowl of soup.