1/4 cup unsalted butter
6 large yellow onions, diced
3 tablespoons dry sherry
1 tablespoon sherry vinegar
4 cups chicken stock
4 cups beef stock
3 sprigs fresh thyme
salt and ground black pepper to taste
6 slices French bread
1/4 cup butter, melted
1 cup grated extra mature Cheddar cheese
1 cup grated Gruyere
Our favourite slutty little soup. French onion. You can never have enough cheese croutons, was tempted to do the whole baguette. Rich, cheesy, and technically healthy as it’s still a ‘soup’. Slut it up to the max - there is folklore that you can chop up a sausage and put it in the soup. We don’t know if anyone has ever dared try this but we wouldn’t be against it in principle.
Preheat oven to 220 degrees C.
Melt 1/4 cup butter in a large, oven-safe pan on medium heat. Stir in onions until they are all coated in butter. Transfer pan to the preheated oven and cook onions, stirring occasionally, until they are tender and well browned, about 1 hour.
Transfer pan to the hob; cook and stir onions over medium heat until they start to brown and stick to the bottom of the pan, about 5 minutes. Pour sherry and vinegar into the pan, and bring to a boil while scraping browned bits of onion off the bottom of the pan with a wooden spoon.
Place caramelised onions in a large soup pot. Pour in chicken stock, beef stock, and thyme. Bring to a boil, skimming off any foam and fat that appear on top. Reduce heat to low and simmer for about an hour. Season with salt and pepper to taste.
Preheat the oven's grill and set the oven rack about 6 inches from the heat source.
Generously brush French bread slices with melted butter. Place on a baking sheet and grill in the preheated oven until crisp and golden, about 5 minutes.
Ladle soup into heat-proof bowls, top each bowl with a piece of toasted bread, sprinkle with 2 to 3 tablespoons of Cheddar cheese and Gruyere cheese.
Grill bowls of soup under the grill until cheese is golden and bubbly, 5 to 6 minutes.