2 (1/2 inch thick) slices French bread, cut into small cubes (about 1 cup)
For the topping:
1/2 cup shredded Swiss cheese
4 (1/2 inch thick) slices French bread
4 slices Gruyere cheese
Instructions:
In a large stock pot, melt butter and oil over medium heat.
Add the onions and sit well to coat in the butter and oil. Cook over medium heat for 30-40 minutes, until browning, stirring occasionally. Continue to cook for an additional 1 hour on medium or medium low, stirring occasionally. (You want the onions to get extremely soft and tender and a deep, rich brown color but not burn.)
Add the sherry and cook for 1-2 minutes to allow some of it to evaporate.
Add the broth, thyme, Worcestershire sauce, salt and black pepper. Stir well. Add the cubed bread and stir to incorporate.
Bring to a boil then reduce heat, cover and simmer on medium low for 30 minutes.
For serving: Carefully transfer the soup to individual ramekins or individual tureens or small oven-proof bowls. Sprinkle with 2 tablespoons of shredded Swiss cheese. Add the slice of French bread on top, then top the bread with Gruyere cheese.
Broil on high heat, about 3-4 inches from the heat source, for 3-4 minutes, until the cheese is melted, being careful not to let it burn. Serve immediately.
(Alternatively, you can place the bread slices on a foil lined baking sheet, top with Gruyere cheese and broil for 2-3 minutes, until melted. Sprinkle the soup bowl with Swiss cheese and serve with the broiled bread slice on top.)