Sour Cream Chocolate Bars

Bring butter, water, and cocoa to boil. Set aside. Combine sour cream and eggs, mixing at medium speed on electric mixer until well-blended. Add butter mixture, mixing at low speed until blended. Gradually add combined dry ingredients, mixing at medium speed until smooth. Spread into greased 15x10x1 inch jelly roll pan. Bake at 350°F (175°C) for 25 to 30 minutes or until wooden pick inserted in center comes out clean. Cool. Frost with Creamy Chocolate Frosting. Creamy Chocolate Frosting: Beat butter, mixing at medium speed of electric mixer. Add combined powdered sugar and cocoa alternately with milk, beating until light and fluffy. Spread over cake, sprinkle with nuts.