1/2 cup (125g) of unsalted butter
4 large yellow onions, thinly sliced
salt and pepper
5 cups (1.25l) vegetable broth
4 beef bullion cubes
2 bay leaves
1/2 lb (250g) Gruyere or Swiss cheese, sliced or shredded
4-5 slices of french bread, toasted
Melt the butter over low heat and add the onions. Cook the onions until they turn a deep, caramel brown. Salt and pepper to taste.
Add the stock, bullion cubes, and bay leaves. Bring to a boil then reduce to a simmer. Cover for 30 minutes.
Discard the bay leaves
Ladle soup in broiler-proof bowls. Add a slice of french bread and cover with cheese. Melt cheese under broiler and serve.