Preheat oven to 325º. Butter and lightly flour a 10 inch tube pan. Sift SWANS DOWN Cake Flour then lightly spoon into measuring cup for 2 ½ cups. Add cocoa, baking soda and salt, sift once more to blend dry ingredients. In a very large bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, beating until well blended. Add vanilla extract, blending well. Gradually add dry cake flour ingredients with sour cream in several additions, blend well but do not over mix (can cause a dry cake). Gradually stir in by hand the boiling water, blend until well incorporated. Pour batter into prepared pan. Bake for approx. 1 hour and 10 minutes or until long tester inserted into middle of cake comes out clean. Cool in pan for approx. 15 minutes or until can handle comfortably. Place cake on rack to complete cooling.
Note: ***Cake is also delicious with a chocolate glaze on top or confectioners’ sugar. ***Cake crumbles easily if removed from pan while still warm; make sure has cooled completely before removing.