Otherwise known as "penuché" icing, butterscotch icing is a great alternative to chocolate or plain sugar icing, particularly for layered sponge cakes. This recipe yields about 360 ml (1 1/2 cups).
Put butter, brown sugar, salt and light cream in the top of a double boiler. Heat and stir until the mixture is smooth.
Remove mixture from heat and cool 5 minutes.
Beat mixture with a hand mixer and gradually add icing sugar and vanilla. Beat until the mixture is spreadable.
If the icing is too thin, set the pan in a large pan of ice water and beat until it's spreadable. If necessary, add more powdered sugar. If you like nuts, try stirring 100 g (1/2 cup) of chopped walnuts or pecans into the icing before spreading. This icing will keep up to three days at room temperature, up to three weeks in the refrigerator or up to six months in the freezer. To store, cover the surface of the icing with a sheet of plastic wrap. When ready to use, soften and stir or beat icing until it is smooth.