1. Heat oven to 350°F. Grease 8- or 9-inch square baking pan.
2. Beat butter and brown sugar blend in large bowl until well blended. Add egg, milk and vanilla; beat well. Stir together flour, baking soda and salt; add to butter mixture, beating until well blended.
3. Set aside 2 tablespoons chocolate chips. Stir the remaining chips and nuts into batter. Spread batter in prepared pan.
4. Bake 15 to 20 minutes or until cake begins to pull from sides of pan, toothpick inserted in center comes out clean and surface is lightly browned. (Do not overbake.) Cool completely in pan on wire rack. (As it cools the center will look underbaked.)
5. Place reserved 2 tablespoons chips and shortening in small microwave-safe bowl. Microwave at MEDIUM (50%) 30 seconds; stir. If necessary, microwave at MEDIUM an additional 10 seconds at at time, stirring after each heating, until chips are melted and smooth when stirred. Drizzle melted chocolate over surface of cake; allow to set. Cut into bars. About 24 bars.