saute the onions in clarified butter until browned. add a little stock, if necessary, to prevent burning.
deglaze the pan with the calvados,add the stock
simmer until the onions are tender and the soup is properly favored
adjust the seasoning with salt and pepper to taste
garnish each portion with a crouton. top generously with grated gruyere or emmenthaler and brown under a salamander or broiler, or bake in a moderate oven until lightly browned