Slice the onion thinly.
Melt butter in a pan and sauté the onions until browned.
Season the onions with salt and pepper.
Add flour and mix well.
Pour in the broth and bring to a boil.
Slice sandwich bread or baguette thinly.
Pour the soup into a bowl and top with bread and cheese.
Finish by melting the cheese using an oven or torch.