Per serving (368g) Calories 528, Fat 28g, Saturates 8.7g, Sugars 16g, Salt 8.9g
In a large saucepan, heat the butter and oil over a medium heat. Add the onions, garlic, thyme, sugar, salt, and pepper. Sauté for around 40-50 minutes, keeping the pot uncovered, until the onions are very tender and caramelized. Stir often to avoid the onions sticking to the pot. If they start to stick, you can add a few splashes of vegetable stock and turn down the heat.
Stir the cornflour into the onions. Turn the heat down to low and cook for another 1-2 minutes. Stir often so the flour doesn't burn.
Add the vegetable stock, yeast extract, and bay leaves. Turn heat back to medium and simmer for 15-20 minutes. Taste the soup to see if it needs any more salt or pepper and add if needed.
Remove the bay leaves from the soup and serve in deep bowls.
To add some crunchy croutons, place 2 slices of toasted baguette onto each bowl and top with grated cheese. Place under the grill until the cheese is bubbling and melted, but not burnt.