Step 1: Prepare Pans and Preheat Oven
Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans thoroughly with butter or cooking spray. Line the bottoms with parchment paper circles, then grease the parchment too. Lightly dust with cocoa powder and tap out the excess. This ensures your cakes release perfectly without sticking.

Step 2: Mix Dry Ingredients
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined and no lumps remain. The thorough mixing ensures even distribution of leavening agents for consistent rise throughout the cake.

Step 3: Combine Wet Ingredients
In a medium bowl or large measuring cup, whisk together the eggs, buttermilk, oil, and vanilla extract until smooth and fully incorporated. The mixture should be homogeneous with no streaks of egg.

Step 4: Bloom the Espresso
Stir the instant espresso powder into the hot coffee until completely dissolved. This “blooms” both the coffee and will bloom the cocoa powder when added, intensifying all the flavors. Let it cool slightly if it’s boiling hot.

Step 5: Mix the Batter
Add the wet ingredients to the dry ingredients and mix with a whisk or electric mixer on low speed just until combined—don’t overmix. The batter will be thick at this point. Now pour in the hot coffee mixture and mix until smooth. The batter will be quite thin and liquid—this is correct! The thin batter is what creates that incredibly moist texture.

Step 6: Bake the Cakes
Divide the batter evenly between the prepared pans (use a kitchen scale for precision if you have one). Bake for 30-35 minutes, until a toothpick inserted in the center comes out clean or with just a few moist crumbs, and the cake springs back when lightly pressed. The cakes should pull away slightly from the pan edges.

Step 7: Cool Completely
Let the cakes cool in the pans for 10 minutes, then run a knife around the edges and invert onto cooling racks. Peel off the parchment paper and let cool completely before frosting—at least 1 hour. If you try to frost warm cakes, the buttercream will melt into a mess.

Step 8: Make the Mocha Buttercream
In a large bowl, beat the softened butter with an electric mixer on medium-high speed for 3-4 minutes until light, fluffy, and pale in color. Dissolve the espresso powder in 2 tablespoons of the heavy cream. Sift together the powdered sugar and cocoa powder. Add half of the sugar mixture to the butter and beat on low speed until incorporated. Add the espresso mixture, vanilla, salt, and remaining cream, then beat until smooth. Add the remaining sugar mixture and beat on low, then increase to medium-high and beat for 3-4 minutes until light and fluffy.

Step 9: Assemble the Cake
If your cakes have domed tops, use a serrated knife to level them off for flat, even layers. Place one cake layer on a serving plate or cake board. Spread about 1 cup of buttercream on top, creating an even layer all the way to the edges. Place the second cake layer on top, pressing down gently. Apply a thin “crumb coat” of frosting all over the cake to seal in crumbs, then refrigerate for 15 minutes. Finish with the remaining frosting, smoothing it with an offset spatula.

Step 10: Decorate and Serve
Garnish with chocolate shavings, chocolate-covered espresso beans, or a dusting of cocoa powder if desired. For clean slices, use a sharp knife dipped in hot water and wiped dry between each cut. Serve at room temperature for the best flavor and texture.