Fillets of Sole Prosper Montagné

This is an adaptation, using American ingredients, of the dish created by Prosper Montagne under the name of Sole Sylvestre. Fino or Amontillado sherry, white port, or Sercial Madeira may be used for the sauce. Positively no vermouth belongs in this recipe and please use butter and true heavy cream. This is a once in a while treat for a celebration, and must be enjoyed as conceived by its creator. I have extended the six-line recipe of Prosper Montagne, so it will make sense to any cook.