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.
Sour Cream Chocolate Frosting
To make the frosting, beat the butter until light and creamy, then beat in the sour cream.
Add about half of the sugar and beat until creamy. Beat in cocoa powder, salt and vanilla until it's as smooth as you can get it, scaping the side of the bowl. Gradually add remaining sugar and enough half & half to make the icing spreadable.
Beat on medium, increasing speed gradually and adjusting liquid as needed, then beat on high until light and fluffy.