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Cocoa Layer Cake with Chocolate Buttercream

A hot-water cocoa batter gives this two-layer chocolate cake a moist, tender crumb beneath smooth, fluffy chocolate buttercream.
A smooth chocolate-frosted layer cake with one slice removed rests on a cake stand.

This is a straightforward chocolate layer cake built from pantry ingredients and careful timing. The key is to mix only as far as each step needs, then frost only when the layers have fully cooled.

A thin batter bakes moist

Boiling water blooms the cocoa and creates an unusually fluid batter. That is expected; it bakes into layers with a tender, moist crumb rather than a dense one.

Prepare every surface

Parchment protects the cake bottoms, while a dusting of cocoa keeps the sides from leaving white flour marks. Taking a minute to prepare both pans makes turning out the layers calm and clean.

Glossy chocolate batter fills two parchment-lined round cake pans before baking.
The glossy chocolate batter is divided between cocoa-dusted, parchment-lined cake pans.

Cool before frosting

Warm cake layers soften buttercream quickly, which makes a cake slide or tear. Leave them on the rack until cool throughout, not merely cool at the surface.

Frost with a light hand

Whip the buttercream until it feels airy and spreadable, then use an offset spatula to keep the layers level. A short rest after frosting firms the finish enough for clean slices.

A chocolate cake slice reveals moist cocoa layers separated by fluffy chocolate buttercream.
A cut slice shows the cake's moist dark crumb and thick chocolate buttercream layers.

Cocoa Layer Cake with Chocolate Buttercream

12 slices
135 minutes total

Ingredients

  • •  2 cups all-purpose flour
  • •  1 3/4 cups granulated sugar
  • •  3/4 cup unsweetened cocoa powder
  • •  1 1/2 tsp baking powder
  • •  1 1/2 tsp baking soda
  • •  1 tsp fine salt
  • •  2 large eggs, at room temperature
  • •  1 cup whole milk
  • •  1/2 cup neutral oil
  • •  1 cup boiling water
  • •  1 1/2 cups unsalted butter, powdered sugar, cocoa powder, and vanilla extract

Method

  1. Prepare the pans

    Heat the oven to 350 F, grease two 8-inch round cake pans, line the bottoms with parchment, and dust the sides lightly with cocoa powder.

    Look for: The parchment lies flat and the pan sides have an even cocoa coating.

  2. Whisk the dry ingredients

    Whisk the flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt in a large bowl until the cocoa has no dark clumps.

    Look for: The dry mixture is one even chocolate-brown color.

  3. Add the wet ingredients

    Whisk in the room-temperature eggs, whole milk, and neutral oil until smooth, scraping the bowl bottom once to incorporate all of the flour.

    Look for: The batter is smooth and no dry flour remains around the bowl edge.

  4. Finish the batter

    Slowly whisk in the boiling water until the thin batter is glossy, then stop mixing immediately so the cake stays tender.

    Look for: The batter pours easily and looks glossy without streaks.

  5. Bake the layers

    Divide batter evenly between the prepared pans and bake at 350 F until the centers spring back and a tester comes out with a few moist crumbs.

    Look for: The layers pull slightly from the pan sides and spring back when touched.

  6. Cool completely

    Cool the cakes in their pans for 10 minutes, turn them onto a wire rack, peel away the parchment, and cool completely before frosting.

    Look for: The layers feel cool all the way through and release cleanly from the parchment.

  7. Whip the buttercream

    Beat the unsalted butter until pale and fluffy, then beat in powdered sugar, cocoa powder, vanilla extract, and 2 to 3 tbsp milk until spreadable.

    Look for: The buttercream is light, smooth, and holds a soft peak on the spatula.

  8. Fill and frost

    Set one cake layer on a plate, spread on a thick layer of buttercream, add the second layer, and frost the top and sides with an offset spatula.

    Look for: The layers are level and the frosting forms an even coat without exposed cake.

  9. Set and slice

    Let the frosted cake stand for 15 minutes so the buttercream firms slightly, then slice with a warm dry knife for clean portions.

    Look for: The frosting no longer smears when the knife begins a slice.