Ingredients
Cake
- 2 cups all-purpose flour 240 g, spooned and leveled
- 325 g granulated sugar about 1 5/8 cups
- 65 g natural unsweetened cocoa powder about 3/4 cup; not sweetened drinking chocolate
- 1 1/4 teaspoons baking powder 5 g
- 1 teaspoon baking soda 5 g
- 2/3 teaspoon fine salt 4 g
- 1 cup cultured low-fat buttermilk 240 ml
- 2 large eggs about 100 g without shells
- 1/2 cup canola oil 120 ml, about 110 g
- 2 teaspoons vanilla extract about 8 g
- 3/4 cup hot water 180 ml
Cocoa buttercream
- 3/4 cup unsalted butter 170 g, softened
- 260 g powdered sugar about 2 1/4 cups, sifted
- 45 g natural unsweetened cocoa powder about 1/2 cup, sifted
- 1/4 cup whole milk 60 ml; add gradually as needed
- 1 teaspoon vanilla extract about 5 g
- 1 g fine salt a scant 1/4 teaspoon
Equipment
- 1 9-by-13-inch metal cake pan at least 2 inches deep
- 2 Mixing bowls
- 1 Whisk
- 1 electric hand mixer
- 1 Wire cooling rack
- 1 flexible spatula
Instructions
Bake the cake
- Heat the oven to 350°F (175°C), with a rack near the center. Line a 9-by-13-inch metal pan, at least 2 inches deep, with parchment across the base and sides. Leave a little overhang if you plan to lift the cake out.
- Whisk flour, sugar, cocoa, baking powder, baking soda and salt in a large bowl, breaking up cocoa lumps. In another bowl whisk buttermilk, eggs, oil and vanilla. Add the wet mixture to the dry and whisk just until combined. Slowly stir in the hot water. Scrape the bowl's bottom and sides; the finished batter should be pourable.
- Pour the batter into the prepared pan. Bake for about 30–38 minutes, until the center is set and a toothpick comes out without wet batter; a few moist crumbs are fine. Begin checking at 30 minutes and avoid overbaking.
- Place the pan on a rack and let the cake cool completely, about 2 hours or longer if needed. Do not frost while the cake or pan still feels warm.
Frost and serve
- Beat the softened butter with an electric mixer until smooth. Add sifted powdered sugar and cocoa in several additions on low speed. Add vanilla, salt and about half the milk. Beat until creamy, then add more milk a teaspoon at a time as needed for a soft, spreadable frosting; you may not need all of it.
- Spread frosting over the cooled cake, making broad swirls with a spoon or spatula. Cut into 15 squares, three rows by five columns. Keep the frosted cake covered in the refrigerator and use within 4 days; let individual slices soften briefly before serving.
Nutrition
Serving: 1 square (1/15 cake)Calories: 394kcalCarbohydrates: 56.6gProtein: 4.7gFat: 18.6gSaturated Fat: 7.3gPolyunsaturated Fat: 2.6gMonounsaturated Fat: 8gCholesterol: 50mgSodium: 286mgPotassium: 173mgFiber: 3.1gSugar: 40gCalcium: 67mgIron: 1.9mg
Video
Notes
Video credit: Preppy Kitchen’s “Amazing Chocolate Cake” demonstrates chocolate batter and buttercream techniques using a layer cake. This card instead makes one rectangular cake with different quantities, natural cocoa and water, and no cacao-nib decoration. Follow the card’s pan, formula and baking cues; do not use the video’s layer-pan timing for this sheet cake.
Nutrition is an ingredient-based estimate per one-fifteenth of the frosted cake using USDA SR Legacy entries: 240 g flour, 325 g granulated sugar, 110 g total cocoa, 5 g baking powder, 5 g baking soda, 5 g total salt, 245 g low-fat buttermilk, 100 g egg, 110 g canola oil, 13 g total vanilla, 170 g butter, 260 g powdered sugar and 62 g whole milk. Water contributes no energy. Estimates include all frosting milk, even if you need less, and exclude decorations. Brand variation and cooking affect the result; cooking-sensitive vitamins and unavailable trans-fat values are not estimated.
Freeze cooled unfrosted portions, well wrapped, for up to 2 months for best quality. Thaw wrapped in the refrigerator and frost after thawing. Refrigerate the frosted cake; storage guidance for other frostings may differ.
