In a kettle melt the butter and in this cook the onions over a medium heat, stirring until the onions are golden. Add 12 cups of cold water, and then add the remaining ingredients. Bring the mixture to a boil and simmer, uncovered, for 2 hours. Strain the stock through a fine sieve into a bowl and let it cool. Chill the stock and remove the fat.
Consomme is nothing more than stock that has been clarified so that it is clear and sparkling.
After the grease has been spooned off the surface of the stock, remove whatever fat that remains by skimming the surface with absorbent paper toweling. In a saucepan combine the stock, egg and egg shell. On the lowest possible flame, and without stirring, bring the mixture to a bare simmer, making absolutely sure that a boil is not attained. Continue this gentle simmer for 10 - 12 minutes. Very gently remove from the flame and let cool for 30 - 45 minutes.