Nigella's chocolate fudge cake is rich, decadent, and iced to the heavens with rich chocolate fudge frosting. Each bite is filled with blissful chocolatey goodness and tender cake.
Preheat the oven to 350 degrees F. Butter and line the bottom of 2 (8-inch) cake pans.
In a large bowl, mix together the flour, sugars, cocoa, baking powder, baking soda and salt.
In another bowl or wide-necked measuring cup whisk together the eggs, sour cream and vanilla until blended.
Using a standing or handheld electric mixer, beat together the melted butter and corn oil until just blended (you'll need another large bowl for this if using the hand mixer; the standing mixer comes with its own bowl), then beat in the water. Add the dry ingredients all at once and mix together at a slow speed. Add the egg mixture, and mix again until everything is blended and then pour into the prepared pans.
Bake the cakes for 25 to 30 minutes, or until a cake-tester comes out clean. Cool the cakes in their pans on a wire rack for 15 minutes, and then turn the cakes out on the rack to cool completely.
Icing
Melt the chocolate in the microwave - 2 to 3 minutes on medium should do it - or in a bowl sitting over a pan of simmering water, and let cool slightly.
In another bowl beat the butter until it's soft and creamy and then add the sifted confectioners' sugar and beat again until everything's light and fluffy. Gently add the vanilla and chocolate and mix together until everything is glossy and smooth.
Sandwich the middle of the cake with about a quarter of the icing, and then ice the top and sides, too, spreading and smoothing with a rubber spatula.
Notes
Properly measuring your flour is the key to success when it comes to baking. To do so, measure your flour using the scoop and sweep method. Aerate the flour with a spoon, then scoop the flour into a measuring cup until it is slightly overflowing. Then, take the flat end of a butter knife and gently sweep it across the top to level it. Never scoop flour straight from the bag and do not tap the measuring cup to pack in the flour. Doing either of those two things is typically the main culprit for dry, dense cake - which we definitely don't want.
Try not to use anything less than 70% dark cocoa solids for the frosting as it adds incredible decadence. Lindt or Ghirardelli are great options. This recipe will yield enough icing to frost the entire cake, you can cut it in half if you only want to ice in between the layers and the top portion. Otherwise, you can always pop any leftovers in an air-tight container and freeze it for later use.
Using sour cream in cake adds a lot of moisture, I wouldn't suggest leaving it out or substituting it.
Store your fudge cake in an air-tight container or on a cake stand fitted with a lid. Keep at room temperature for up to 4 days. You do not need to refrigerate this cake. If transporting, I suggest using a cake carrier (which you can also use for storage).
You can prepare and freeze the unfrosted cake layers. Individually wrap the two cake layers in plastic wrap followed by a layer of aluminum foil. Store in the freezer for up to 3 months and thaw at room temperature, unwrapped.