This sauce must be served warm because it becomes much too thick when cold or even at room temperature. It is particularly good over ice cream. Reheat leftover sauce over simmering water.
Thoroughly combine the cocoa powder, brown sugar, and granulated sugar.
Place the cream, butter, and salt in a saucepan over low heat. Melt the butter in the cream and bring the mixture to scalding.
Whisk in the sugar and cocoa mixture gradually to avoid lumps. Cook over low heat, stirring constantly with the whisk, until the sugar has dissolved and t