This icing is a pale coffee color with a creamy brown sugar flavor.
Heat, stirring, in the top of a double boiler until the mixture is smooth:
      4 tablespoons unsalted butter
      1/2 cup packed light or dark brown sugar
      1/8 teaspoon salt
      1/3 cup light cream or evaporated milk
Remove from the heat and let cool for about 5 minutes. Gradually add, beating until spreadable:
      2 cups powdered sugar, sifted if lumpy
      1/2 teaspoon vanilla or 1 teaspoon rum
If the icing seems thin, set the pan in a larger pan of ice water and beat until spreadable. If necessary, add more:
      Powdered sugar (optional)
Stir in:
      1/2 cup chopped walnuts or pecans (optional)
To store, cover the surface of the icing with a sheet of plastic wrap. This keeps for up to 3 days at room temperature or up to 3 weeks refrigerated. Or freeze for up to 6 months. Soften and stir or beat until smooth before using.