Heat the butter in a saucepan and add the onions and shallots cut into rings. If the onions have germs inside, remove them, if necessary cut the onion in half and cut into half rings, it tastes just as good. Fry the onions for about 10 minutes while stirring frequently, but do not let them brown. Pour in the broth and wine and slowly bring the soup to a boil. Season to taste with fleur de sel and pepper, using more white pepper than black pepper. Cover and simmer on a low flame for another 15 minutes.
In the meantime, toast the bread brown in a pan without fat. Pour the soup into fireproof cups or bowls, cover each with a slice of toasted bread and sprinkle with the Gouda.
Bake in a preheated oven at 250 ° top heat for 4 - 6 minutes.