Slice 4-5 large onions and saute in a tbsp of butter until shiny. deglaze with half a bottle of dry white wine and let simmer for 3 minutes, add salt, and pepper such as 1l of vegetable stock, and leave it on medium heat for approx 30 minutes.
In the meantime slice some white bread, cover it with grated cheese  (fi gruyere) and bake for ca 10 minutes, serve the soup hot with croutons in it.
Bon appetit!