Though it is called a sauce, it is neither a liquid nor smooth. It could be more accurately classified as a spread and has the consistency of butter. It is easy to make and keeps for months under refrigeration. It can be pressed into a decorative mold before chilling.
Under European Community regulations, to be called rum/brandy/sherry butter, it must contain at least 20% butterfat.
^"Commission Regulation (EC) No 445/2007 of 23 April 2007 laying down certain detailed rules for the application of Council Regulation (EC) No 2991/94 laying down standards for spreadable fats and of Council Regulation (EEC) No 1898/87 on the protection of designations used in the marketing of milk and milk products"