1. Heat oven to 350 F. Grease and flour 13x9x2-inch baking pan.
2. Combine chocolate chips, butter and water in large mixer bowl; stir with spoon until chocolate is melted and mixture is blended. Gradually add flour, sugar, sour cream, eggs, baking soda, salt and vanilla; beat on low speed of electric mixer until smooth. Pour batter into prepared pan.
3. Bake 35 to 40 minutes or until wooden pick inserted in center of cake comes out clean. Cool completely in pan on wire rack. Frost with SPECIAL DARK FROSTING. 12 to 15 servings.
SPECIAL DARK FROSTING
1/4 cup (1/2 stick) butter or margarine
1 cup HERSHEY'S SPECIAL DARK Chocolate Chips
1-1/2 cups powdered sugar
1/4 cup milk
1/2 teaspoon vanilla extract
Place butter and chocolate chips in medium microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. If necessary, microwave at MEDIUM 15 seconds at a time, stirring after each heating, until chips are melted and mixture is smooth when stirred. Gradually beat in powdered sugar, milk and vanilla, beating until smooth. If necessary, refrigerate 5 to 10 minutes or until of desired spreading consistency. About 1-2/3 cups frosting.
VARIATION: For a stronger chocolate flavored cake, decrease flour to 2 cups and add 1/3 cup HERSHEY'S Cocoa.