Preheat oven to 350 degrees F. Grease and flour 2 9-inch round cake pans.
In a large mixing bowl, stir or sift together the sugar, flour, baking soda & baking powder, salt and cocoa powder.
Stir in half & half, eggs, oil and vanilla until very well mixed (I do this with a heavy duty spatula scraper), then stir in coffee. Batter will be wet and soupy looking.
Pour into pans and bake for 35 minutes or until cakes test done. Let cool on rack for 10 minutes, then flip from pan and cool completely before frosting.
To make the frosting, beat the softened butter and about half of the sugar until creamy. Beat in sour cream and cocoa powder until smooth. Gradually add remaining sugar and enough half & half to make the icing spreadable.