Sift sugar, flour, baking soda and salt together into a large mixing bowl. In a separate bowl, blend the hot coffee, sour cream, and vegetable oil with whisk. With the mixer on low speed, add the coffee mixture in a stream to the dry ingredients and mix until blended, about 35 seconds. Stop mixer to scrape the bowl several times with spatula. Add eggs one at a time and mix on medium-low speed after each addition until smooth, about 15 seconds.
Scrape bowl each time.
Add chocolate and mix until batter is uniform in color, about 10 seconds. Divide batter evenly between pans and place on center rack in oven. Cool layers in the pans on a rack. Fudge Filling 2 oz. Mixture will be smooth and velvety.