Put the onions into cold water, and remove their skins. Then put them into a saucepan, and cover with a soup stock (Pot-au-feu or Bouillon), if you have it, otherwise use water, and let them stew slowly for an hour and a half, till they are almost falling to pieces. Then drain the Onions through a colander, and save the stock. Put three tablespoonfuls of butter into a frying pan, and add three tablespoonfuls of flour, and make a light brown Roux. When brown, add a half pint of the broth in which the Onions were boiled. Season well with salt and pepper and a dash of Cayenne. Put the Onions into this and let them simmer gently for about twenty minutes longer. Serve hot.