1. Heat oven to 350°F. Grease and flour 15-1/2x10-1/2x1-inch jelly-roll pan.
2. Combine water, butter and cocoa in small saucepan. Cook over medium heat, stirring occasionally, until mixture boils; boil and stir 1 minute. Remove from heat; set aside.
3. Stir together flour, sugar, baking soda and salt in large bowl. Add eggs and sour cream; beat until well blended. Add cocoa mixture; beat just until blended (batter will be thin). Pour into prepared pan.
4. Bake 25 to 30 minutes or until wooden pick inserted in center comes out clean. Do not remove cake from pan; spread peanut butter over warm cake. Cool completely in pan on wire rack. Prepare CHOCOLATE TOPPING; carefully spread over top, covering peanut butter. Allow topping to set; cut into squares. 20 to 24 servings.
CHOCOLATE TOPPING: Place 2 cups (12-oz. pkg.) HERSHEY'S SPECIAL DARK Chocolate Chips or HERSHEY'S Semi-Sweet Chocolate Chips and 2 tablespoons shortening (do not use butter, margarine, spread or oil) in small microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, just until chips are melted when stirred.