In a large bowl, cream 1 1/3 cups sugar with 1/2 cup butter or margarine, and salt. Blend extract, 2 tablespoons milk, and remaining sugar into mixture. Gradually stir remaining milk into frosting until desired spreading consistency is reached.
Melt and stir unsweetened chocolate and 2 tablespoons butter or margarine together in a microwave, or in a double boiler. Double this glaze if desired.
Frost cake. Pipe a frosting scallop at the top edge of the cake to keep glaze from dripping down the sides of the cake. Pour the glaze over the top of the cake. Chill until glaze has set.
