To prepare frosting, melt butter in saucepan over medium heat and stir in brown sugar and cream. Bring to a boil, then transfer to a mixing bowl. Add confectioners' sugar and vanilla. Beat with a handheld electric mixer until it reaches a spreading consistency. At this time it may be necessary to add a tablespoon of heavy cream, or more, if frosting gets too thick. Just be sure to add cream in small amounts because you can always "add to," but you can't take away. Frost your cake and sprinkle the top with chopped nuts, if desired.
Cook's Note: To fix "runny icing," add additional powdered sugar until the consistency is right.