Preheat oven to 325. Grease and flour 10 inch tube or bundt pan
In large bowl cream the butter, gradually add sugar, beating well.
Add the room temperature eggs, one at a time, beating well with the electric mixer 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 tube or bundt pan.
Bake at 325 for 1 hour and 20 minutes (give or take 5 minutes depending on your oven) or until cake tests done.
Cool cake in pan for 10 to 15 minutes, remove from pan and cool cake completely on wire rack before serving or serve immediately with your favorite ice cream or hot chocolate sauce or icing. It will melt in your mouth.