enough for one cake roll
4 (1-ounce) squares unsweetened chocolate
1/4 cup butter or margarine
1/3 cup milk
1/8 teaspoon salt
3 cups sifted powdered sugar
1 teaspoon vanilla extract
Combine first 4 ingredients in top of a double boiler; place over boiling water, stirring constantly, until chocolate and butter are melted. Remove from heat and cool.
Add powdered sugar and vanilla to cooled mixture; beat until smooth.