Vanilla Sauce (with Cognac)

Stir 2 tablespoonfuls butter with 6 tablespoonfuls powdered sugar to a cream; add by degrees 3 tablespoonfuls Cognac, sherry or Madeira wine and ½ cup boiling water; keep beating all the time; put this in a tin pail and set in a vessel of hot water; keep stirring until hot, but do not allow it to boil; remove from the fire and add 2 teaspoonfuls vanilla essence.