Moist Chocolate Buttermilk Cake
Chocolate buttermilk cake mixed by hand in one bowl and baked in a single 9x13 pan. A cup of hot coffee poured in at the end blooms the cocoa, and the buttermilk keeps the crumb tender for days. Finished with a soft cocoa buttermilk frosting and a scatter of chopped walnuts.
Ingredients
Cake Batter
- 2 cups all-purpose flour
- 2 cups granulated sugar
- 3/4 cup unsweetened cocoa powder natural, not Dutch-process
- 2 teaspoons baking powder
- 1 teaspoon baking soda
- 1/2 teaspoon salt
- 2 large eggs at room temperature
- 1/2 cup vegetable oil
- 1/2 cup unsalted butter melted and cooled
- 2 teaspoons vanilla extract
- 1 cup buttermilk well shaken
- 1 cup hot coffee or hot water
Cocoa Buttermilk Frosting
- 3 cups powdered sugar sifted, plus more as needed
- 3/4 cup unsalted butter softened
- 1/2 cup unsweetened cocoa powder
- 1 teaspoon vanilla extract
- 1/3 cup buttermilk at room temperature, more as needed
- 1/4 teaspoon fine sea salt
- 1/2 cup chopped walnuts optional, for scattering over the frosting
Equipment
- 9x13-inch Baking Pan
- Large mixing bowl
- Whisk
- Electric mixer or stand mixer (for frosting)
- Offset spatula or butter knife
- Parchment paper (optional)
Instructions
Mix the Batter
- Heat the oven to 350°F (175°C). Grease a 9x13-inch baking pan and line it with parchment paper.
- Measure the flour, granulated sugar and cocoa powder into a large mixing bowl.
- Add the baking powder, baking soda and salt.
- Whisk the dry ingredients together until the color is completely even and no clumps of cocoa remain.
- Make a well in the center and add the eggs, vegetable oil, cooled melted butter, buttermilk and vanilla extract. Whisk gently from the center outward until no dry flour is left. The batter will be thick.
- Pour in the hot coffee in a slow stream while whisking. The batter will thin out and turn glossy, which is correct.
Bake and Cool
- Pour the batter into the prepared pan, smooth the surface, and bake for 30 to 35 minutes, until a toothpick pushed into the middle comes out with a few moist crumbs clinging to it.
- Let the cake cool completely in the pan on a wire rack before frosting it. Warm cake melts buttercream.
Make the Frosting
- Beat the softened butter until creamy, then sift in the cocoa powder and beat until fluffy and dark.
- Add the powdered sugar and buttermilk alternately, starting and ending with the sugar and beating smooth after each addition. Beat in the vanilla and salt until the frosting is shiny and pourable. Add more sugar or buttermilk to adjust.
Frost and Serve
- Pour the frosting over the cooled cake while it is still freshly beaten and loose.
- Spread it to the edges with an offset spatula and scatter the chopped walnuts over the top while the surface is still tacky.
- Chill the frosted cake for 15 to 20 minutes to set the frosting, then cut into 12 squares and serve.
Notes
* Make-ahead: bake the cake a day early, cover the cooled pan tightly with foil and frost it on the day you serve. The crumb is at its best on the second day.
* Storage: covered at room temperature for 2 days, or in the refrigerator for 4 to 5 days. Press plastic wrap against the cut faces, not just over the top.
* Freezing: wrap the unfrosted slab in plastic then foil and freeze up to 2 months, thawing overnight still wrapped. Frosted slices freeze well once the buttercream has set firm on a tray. * Cocoa: use natural cocoa powder, not Dutch-process. The baking soda is measured to react with the acid in natural cocoa, and Dutch-process is alkalized.
* Substitutions: hot water swaps in for the hot coffee, and a cup of milk with 1 tablespoon of lemon juice stirred in stands in for the buttermilk.
* Doneness: a toothpick should come out with a few moist crumbs clinging to it, never clean.
* Nutrition values are an estimate.
* Storage: covered at room temperature for 2 days, or in the refrigerator for 4 to 5 days. Press plastic wrap against the cut faces, not just over the top.
* Freezing: wrap the unfrosted slab in plastic then foil and freeze up to 2 months, thawing overnight still wrapped. Frosted slices freeze well once the buttercream has set firm on a tray. * Cocoa: use natural cocoa powder, not Dutch-process. The baking soda is measured to react with the acid in natural cocoa, and Dutch-process is alkalized.
* Substitutions: hot water swaps in for the hot coffee, and a cup of milk with 1 tablespoon of lemon juice stirred in stands in for the buttermilk.
* Doneness: a toothpick should come out with a few moist crumbs clinging to it, never clean.
* Nutrition values are an estimate.
Nutrition
Calories: 470kcal | Carbohydrates: 68g | Protein: 5g | Fat: 22g | Saturated Fat: 11g | Cholesterol: 70mg | Sodium: 340mg | Potassium: 180mg | Fiber: 3g | Sugar: 49g | Vitamin A: 500IU | Calcium: 70mg | Iron: 2.4mg