1. Heat oven to 350°F. Grease and flour 12-cup fluted tube pan.
2. Beat butter, sugar, eggs and vanilla in large bowl until fluffy; beat in sour cream. Stir baking soda into buttermilk; set aside. Stir together flour, cocoa and salt; add alternately with buttermilk mixture to butter mixture. Beat 2 minutes on medium speed of mixer. Pour batter into prepared pan.
3. Bake 45 to 50 minutes or until wooden pick inserted comes out clean. Cool 10 minutes; remove from pan to wire rack. Cool completely. Place cake on serving plate. Sift powdered sugar on top and sides of cake. Serve with blueberries, strawberries and whipped cream , if desired. 12 to 16 servings.
* To sour milk: Use 1 tablespoon white vinegar plus milk to equal 1 cup.