Ingredients
- 80g butter or ghee
- 1tbs olive oil
- 1.5kg onions, thinly sliced
- Sea salt and black pepper
- 100ml dry sherry
- 1½ litres beef stock (home-made or a good-quality shop bought)
- 1 bay leaf
- 1tbs Dijon mustard
- 1 loaf rustic sourdough bread, thickly sliced
- 450g Gruyère cheese, grated
Melt the butter and olive oil in a large pan over a medium-high heat. Add the onions and cook, stirring regularly until they begin to soften. Lower the heat and cook until the onions are very sweet and golden-brown. You will need to stir them regularly and it can take one to two hours. Add a tablespoon of water if they begin to stick too much.
Season with salt and pepper. Add the sherry and bring to a simmer, scraping any brown bits as you stir. Leave to simmer for a minute before adding the bay leaf and stock. Leave to simmer for 20 minutes. Taste for seasoning.
Meanwhile, grill the thickly sliced bread on one side. Butter the untoasted side and spread thinly with a little Dijon mustard. Sprinkle the grated cheese on top of the toast.
