Let’s embark on making this impressive Dark Chocolate Honeycomb Cake! It involves several stages, so plan your time accordingly.

Make the Chocolate Cake Layers: Preheat oven to 350°F (175°C). Grease three 6-inch round cake pans, dust them with cocoa powder (tapping out excess), and line the bottoms with parchment paper rounds. In the large bowl of your stand mixer (or a large mixing bowl), whisk together the flour, granulated sugar, cocoa powder(s), baking soda, baking powder, and salt until well combined.

In a separate medium bowl, whisk together the 2 room temperature eggs, 1/4 cup vegetable oil, 3/4 cup buttermilk, and 2 teaspoons vanilla extract. Very carefully and slowly pour the 3/4 cup very hot water into this wet mixture while whisking constantly until blended.

Add the wet ingredients to the dry ingredients in the mixer bowl. Mix on low speed to combine, then increase to medium speed and beat for 2-3 minutes until the batter is smooth. Scrape down the sides as needed. The batter will be very thin.

Pour the batter evenly among the three prepared pans. Bake for approximately 30-35 minutes, or until a wooden toothpick inserted into the center comes out with just a few moist crumbs attached (or mostly clean). Place the cake pans on wire racks to cool for 10 minutes. Then, carefully invert the cakes onto the wire racks, peel off the parchment paper, and let them cool completely.

Make the Honeycomb: While the cakes bake/cool, make the honeycomb. Line a quarter sheet pan (9×13 inches) with a silicone baking mat or heavily greased heavy-duty foil. Have your sifted 1 tablespoon of baking soda ready nearby.

In a large, heavy-bottomed saucepan with high sides, combine the 2 cups granulated sugar, 1/2 cup light corn syrup, and 1/3 cup water. Stir over medium-high heat just until the sugar is dissolved. Once dissolved, stop stirring completely. Bring the mixture to a boil. Attach your candy thermometer to the side of the pan, ensuring the tip is submerged but not touching the bottom. Use a pastry brush dipped in water to wash down any sugar crystals clinging to the sides of the pan.

Boil the mixture, without stirring, until the temperature reaches exactly 300°F (150°C) on the candy thermometer (hard crack stage). This will take about 10 minutes, watch it closely! Immediately remove the saucepan from the heat. Quickly sprinkle the sifted baking soda all over the surface of the hot syrup and whisk it in very briefly (max 5 seconds) – just enough to incorporate. The mixture will foam up dramatically! Do not overwhisk, or it will deflate.

Immediately pour the foaming mixture onto the prepared silicone mat or greased foil in the sheet pan. Do not spread it. Allow the honeycomb to cool completely at room temperature without disturbing it (this takes 1-2 hours). Once completely cool and hard, carefully break it into large shards for decoration. Take some smaller pieces or shards and chop them finely or crush them in a bag to use between the cake layers. Store honeycomb pieces in an airtight container at room temperature, separated by parchment if needed, until ready to assemble (humidity is the enemy!).

Make the Chocolate Frosting: In a medium bowl, whisk together the sifted 3 cups powdered sugar, 1 cup regular cocoa powder, and optional 3 tablespoons black cocoa powder. In the clean bowl of your stand mixer fitted with the paddle attachment, beat the 1 1/2 cups room temperature butter on medium speed until smooth and creamy, about 1 minute.

Reduce speed to low and gradually add the sugar/cocoa mixture, about 1 cup at a time, mixing well after each addition and scraping the bowl. Once incorporated, beat in the melted and cooled dark chocolate until combined. Add 1 tablespoon of heavy cream and beat on medium-high speed. Add more cream, 1 tablespoon at a time, only if needed, until the frosting reaches a smooth, spreadable consistency. Continue beating on medium-high or high speed for about 5 minutes until the frosting is very smooth and fluffy.

Assemble the Cake: Place one cooled chocolate cake layer onto your cake stand or serving plate. Top with about 2/3 cup of the chocolate frosting and spread it evenly. Sprinkle some of the crushed honeycomb pieces over the frosting.

Place the second cake layer on top, pressing gently. Repeat with another 2/3 cup frosting and more crushed honeycomb. Place the third cake layer on top. Apply a thin layer of frosting all over the cake (top and sides) to create a crumb coat. Refrigerate the cake for about 30 minutes to firm up the crumb coat.

Once chilled, apply the remaining frosting to the sides and top of the cake, creating a smooth or rustic pattern as desired using an offset spatula. Carefully press the larger honeycomb shards decoratively onto the top and/or sides of the cake just before serving. Slice and enjoy!