- In a large non-stick saucepan, brown the onions in the butter until golden and soft, about 30 minutes. Season with salt and pepper. Dust with the flour and cook for 1 more minute. Add the beer and bring to a boil, stirring constantly. Add the broth and bring to a boil. Reduce the heat and simmer for about 10 minutes. Add more broth if necessary. Adjust the seasoning.
- With the rack in the middle position, preheat the broiler.
- Ladle the soup into 4 ovenproof bowls. Place 1 toast in each bowl and top with cheese. Place the bowls on a baking sheet. Broil until the cheese is golden brown.