Preheat oven to 325F.

Cream butter; gradually add sugar, beating well. Add eggs, one at a time, beating well after each addition. Combine flour, cocoa, soda and salt; add to creamed mixture alternately with sour cream, beginning and ending with flour mixture. Mix well after each addition. Add boiling water and mix well. Stir in vanilla. Pour batter into a greased and floured ten-inch tube pan. Bake for one hour and 20 minutes or until tester comes out clean.

Cool cake in pan ten to fifteen minutes; remove from pan and cool completely.