PREHEAT oven to 350° F. Grease two 9-inch-round baking pans or one 13 x 9-inch baking pan.
BEAT sugar, butter and vanilla extract in large mixer bowl. Add eggs; beat for 1 minute. Beat in melted chocolate. Combine flour, baking soda and salt; beat into creamed mixture alternately with milk.
POUR into prepared baking pan(s).
BAKE for 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool for 20 minutes; invert onto wire rack(s) to cool completely.
FROST with Creamy Chocolate Frosting.
FOR CREAMY CHOCOLATE FROSTING:
MICROWAVE butter and baking bar in small, uncovered, microwave-safe bowl on HIGH (100%) power for 45 seconds; STIR. The bar may retain some of its shape. If necessary, microwave at additional 10 to 15-second intervals, stirring just until melted. Cool to room temperature.
BEAT 1 cup sugar, vanilla extract and salt into chocolate mixture until creamy. Gradually beat in remaining sugar alternately with milk until smooth. Makes 2 cups.