1 c. butter
2 c. sugar
1 c. brown sugar, firmly packed
6 lg. eggs
2 1/2 c. all-purpose flour
1/4 tsp. baking soda
1/2 c. cocoa
8 oz. sour cream
2 tsp. vanilla extract

Beat butter at medium speed for 2 minutes. Gradually add sugars, beating at medium speed 5 to 7 minutes. Add eggs, one at a time, beating just until the yellow disappears. Combine flour, baking soda and cocoa; add to creamed mixture alternately with sour cream. Mix at lowest speed until just blended. Add vanilla and mix slightly. Bake at 325 degrees for 1 hour and 20 minutes. Cool in pan 10 to 15 minutes; remove onto plate. If desired, sprinkle with powdered sugar.