In a double boiler, melt the chocolate with the butter. Transfer to a heavy saucepan and combine with the sugar, cream and salt. Over medium-low heat, stirring constantly, bring the mixture to a boil. Allow it to boil slowly, without stirring, for 7 minutes. Remove the sauce from the heat and stir in the sherry and vanilla. Serve warm. Store in the refrigerator. Beat This! by Ann Hodgman Isbn 1-881527-21-2 pg 82