• Preheat the oven to 350°F (175°C). Grease and line three 9-inch round cake pans with parchment paper.
• Combine dry ingredients: In a large mixing bowl, sift together the sugar, flour, cocoa powder, espresso powder, baking soda, baking powder, and salt.
• Mix wet ingredients: In another bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla extract until well combined.
• Combine wet and dry ingredients: Gradually add the wet mixture to the dry ingredients while mixing with a hand mixer on low speed. Mix until just combined.
• Add boiling water: Slowly pour in the boiling water while mixing on low speed. The batter will be thin; this ensures a moist cake.
• Divide batter: Evenly distribute the batter among the prepared cake pans.
• Bake: Place the pans in the oven and bake for 28-32 minutes, or until a toothpick inserted into the center comes out clean.
• Cool: Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Chocolate Frosting

• Cream butter: In a large bowl, beat the softened butter with a hand mixer on medium speed until light and fluffy.
• Add cocoa powder: Gradually add the cocoa powder, beating until smooth.
• Add powdered sugar and milk: Alternate adding powdered sugar and milk in small amounts, mixing on low speed until fully incorporated. Adjust consistency with more milk or sugar if needed.
• Add vanilla: Stir in the vanilla extract and mix until smooth and creamy.

Assembly

• Level cakes: If necessary, level the tops of the cooled cakes with a serrated knife.
• Layer frosting: Place the first cake layer on a serving plate or cake stand. Spread a generous amount of frosting evenly over the top. Repeat with the second and third layers.
• Frost exterior: Use the remaining frosting to coat the sides and top of the cake. Smooth or add decorative swirls as desired.
• Chill or serve: Chill the cake for 30 minutes to set the frosting or serve immediately.