Slice the onions finely and brown them in butter on a low heat. sprinkle with flour and cook gently for 3-4 mn. add dry white wine and reduce by half. Add the chicken or beef stock. season and cook on a low heat for around two hours. Season to taste.
Put the soup into four bowls or a large soup tureen. Sprinkle the croutons* over the top. Sprinkle on a generous amount of the grated emmental. Brown under the grill or salamander. Serve immediately.
*croutons, made using baguette dried out in oven until brown