Chocolate-Sour Cream Pound Cake

1 cup butter or margarine, melted
2 cups granulated sugar
1 cup firmly packed brown sugar
6 large eggs
2 1/2 cups all-purpose flour
1/4 teaspoon baking soda
1/2 cup cocoa
1 (8 ounce) container sour cream
2 teaspoons vanilla extract
Confectioners' sugar (optional)

Beat butter at medium speed with electric mixer about 2 minutes or until soft and creamy. Gradually add sugars, beating at medium speed 5 to 7 minutes. Add eggs, one at a time, beating just until yellow disappears.

Combine flour, baking soda and cocoa; add to creamed mixture alternately with sour cream, beginning and ending with flour mixture. Mix at lowest speed just until blended after each addition; stir in vanilla extract.

Spoon batter into greased and floured 10-inch tube pan. Bake at 325 degrees F for 1 hour and 20 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on wire rack 10 to 15 minutes; remove from pan, and cool completely on wire rack. Sprinkle with confectioners' sugar, if desired.