This cake has buttermilk, espresso, and some really good high end cocoa that sets it apart from any you have made from a box, this is STUPID good chocolate cake! I use Ghiradelli Majestic cocoa, you find it on ebay (22% - 24% cocoa fat) or some Gherkens Garnet cocoa also high in cocoa fat, this seems to be the secret weapon to use here, yes you can make it with store shelf Hershey's cocoa but it won't be the same.
I make this single layer cake in a #6 (9") cast iron skillet, I start by placing a bowl upside down on a sheet of parchment paper and cutting around it, I butter the bottom of the skillet, place the parchment paper in the bottom, press out all the air, then butter the whole inside of the skillet, followed by putting half a cup of all purpose flour in the skillet, rolling it around to coat the buttered surface, then tapping out any excess. Turn the oven on to 325F and let preheat.
Ingredients
• 1 cup cake flour
• 1/2 cup natural unsweetened cocoa powder
• 3/4 teaspoon baking soda
• 1/2 teaspoon salt
• 3/4 stick unsalted butter, room temperature
• 1 cup (packed) golden brown sugar
• 1 1/2 large eggs
• 3/4 teaspoon vanilla extract
• 1/2 cup buttermilk
• 2 teaspoons instant espresso powder dissolved in 1/3 cup hot water
• Position rack in center of oven; preheat to 325°F. Generously butter one 9-inch cake pan with 2-inch-high sides; dust with flour, tapping out any excess. Line bottom of pan with parchment paper.
• Sift 1 cup cake flour, cocoa, baking soda, and salt into medium bowl. Using electric mixer, beat butter in large bowl until smooth. Add brown sugar and beat until well blended, about 2 minutes. Add eggs 1 at a time, beating well after each addition. Mix in vanilla. Add flour mixture in 3 additions alternately with buttermilk in 2 additions, beating just until blended after each addition. Gradually add hot espresso-water mixture, beating just until smooth.
• Pour batter in pan, smooth top. Bake cake until tester inserted into center comes out clean, about 40 minutes. Cool cake in pan on rack 15 minutes. Run small knife around sides of pan to loosen cake. Place dinner plate atop skillet, invert skillet and cake will come out onto plate. Cool completely. Warm up frosting in microwave until it spreads easily, frost cake as desired.
A variation I did last one I made, drain liquid from a 10oz jar of maraschino cherries into a mixing cup, pour out liquid until 1/3 cup remains, omit the water and instead use this liquid to make the espresso in the recipe, fold in the cherries into the batter just before pouring batter into the skillet. Baking times will be quite a bit longer, up to 1hr, but oh man it makes it like Black Forest cake!