I have used this recipe from another cake site a few times and everyone have always liked it. There are also some chocolate mud cake recipes here on cc that are dense and taste wonderful.
Triple Chocolate Cappuccino Sour Cream Pound Cake
Sift together and set aside:
3 cups of cake flour
1/4 tsp. baking soda
1/4 tsp. salt
1/2 cup good quality dry cocoa (I used Hershey's)
Bring to room temperature:
6 eggs that have been separated
1 cup sour cream
1 cup real sweet cream butter
1/3 cup of Cappuccino French Vanilla mix (I used Sam's Club brand). Place the dry mix into a glass measuring cup and pour boiling water over it up to the 1/2 cup mark, and let sit to cool off a bit.
2 squares of Baker's semi-sweet baking chocolate squares plus
6 squares Baker's German Sweet chocolate baking bar (will equal 1/3 of the bar) and melt these two together in the microwave at 30 second intervals until melted. Set aside to cool a bit.
1 tsp. real vanilla
3 cups sugar
4 tbs. vegetable oil
Preheat oven to 300 degrees Fahrenheit. Cream together the butter and sugar on low in a stand mixer until completely incorporated and light colored. Keep mixer going and add one egg yolk at a time into the creamed butter and sugar, staying on low speed. You don't want any air beat into this batter. Add the vanilla, the cooled down cappuccino mix, and the oil, scraping often. Next the melted chocolates go in, again scraping often to incorporate all of the ingredients. Next, alternate the flour/soda/salt mixture and the sour cream. Keep that mixer on low, and scrape again to insure all ingredients are incorporated into the batter.
Using a hand mixer, beat the egg whites just until they are nice and frothy and starting to hold their shape, but not so much that they are becoming dry-not stiff. With a wire whisk, incorporate the egg whites into the entire batter.
Using a pan release, cover three 8" round pans both bottom and sides. I don't use parchment paper on this cake, but if you feel safer doing so, use that on the bottom of each pan. Bake for approx. 35-45 minutes or until a tooth pick comes out clean. Each oven is slightly different, so check. Once done flip out onto waxed paper or parchment paper that has pan release on it for them to cool before icing.