1 and 3/4 cups (219g) all-purpose flour
3/4 cup (62g) unsweetened natural cocoa powder*
1 and 3/4 cups (350g) granulated sugar
2 teaspoons baking soda
1 teaspoon baking powder
1 teaspoon salt
2 teaspoons espresso powder (optional)*
1/2 cup (120ml) vegetable oil (or canola oil or melted coconut oil)
2 large eggs, at room temperature*
2 teaspoons pure vanilla extract
1 cup (240ml) buttermilk, at room temperature*
1 cup (240ml) freshly brewed strong hot coffee (regular or decaf)*
1.25 cups (2.5 sticks or 290g) unsalted butter, softened to room temperature
3 and 1/2 cups (420g) confectioners’ sugar
3/4 cup (65g) unsweetened cocoa powder (natural or dutch process)*
3–5 Tablespoons (45-75ml) heavy cream (or half-and-half or milk), at room temperature
1/4 teaspoon salt
1 teaspoon pure vanilla extract
optional for decoration: semi-sweet chocolate chips
Preheat oven to 350°F (177°C). Grease two 9-inch cake pans, line with parchment paper, then grease the parchment paper. Parchment paper helps the cakes seamlessly release from the pans.
Make the cake: Whisk the flour, cocoa powder, sugar, baking soda, baking powder, salt, and espresso powder (if using) together in a large bowl. Set aside. Using a handheld or stand mixer fitted with a whisk attachment (or you can use a whisk) mix the oil, eggs, and vanilla together on medium-high speed until combined. Add the buttermilk and mix until combined. Pour the wet ingredients into the dry ingredients, add the hot water/coffee, and whisk or beat on low speed until the batter is completely combined. Batter is thin.
Divide batter evenly between pans. Bake for 23-26 minutes or until a toothpick inserted in the center comes out clean. Baking times vary, so keep an eye on yours. The cakes are done when a toothpick inserted in the center comes out clean. (Note: Even if they’re completely done, the cooled cakes may slightly sink in the center. Cocoa powder is simply not as structurally strong as all-purpose flour and can’t hold up to all the moisture necessary to make a moist tasting chocolate cake. It’s normal!)
Remove the cakes from the oven and set on a wire rack. Allow to cool completely in the pan.
Make the buttercream: With a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy – about 2 minutes. Add confectioners’ sugar, cocoa powder, 3 Tablespoons heavy cream, salt, and vanilla extract. Beat on low speed for 30 seconds, then increase to high speed and beat for 1 full minute. Do not over-whip. Add 1/4 cup more confectioners’ sugar or cocoa powder if frosting is too thin or 1-2 more Tablespoons of cream if frosting is too thick. (I usually add 1 more.) Taste. Add another pinch of salt if desired.
Assemble and frost: If cooled cakes are domed on top, use a large serrated knife to slice a thin layer off the tops to create a flat surface. This is called “leveling” the cakes. Discard or crumble over finished cake. Place 1 cake layer on your cake stand or serving plate. Evenly cover the top with frosting. Top with 2nd layer and spread remaining frosting all over the top and sides. I always use an icing spatula and bench scraper for the frosting. Garnish with chocolate chips, if desired.
Refrigerate cake for at least 30-60 minutes before slicing. This helps the cake hold its shape when cutting.
Cover leftover cake tightly and store in the refrigerator for up to 5 days.