For the cake:
- 126 g or 4 ½ oz unsweetened cocoa (Dutch-processed)*
- 472 g or 2 c boiling water
- 6 large eggs
- 18 g or 4 ½ tsp vanilla
- 470 g or 16 ½ oz sifted cake flour
- 600 g or 3 c granulated sugar
- 20 g or 6 tsp baking powder
- 10 g or 1 ½ tsp fine sea salt
- 454 g or 16 oz unsalted butter, softened
For the frosting:
- 3 large egg yolks
- 2 large eggs
- 6 g or ¾ tsp kosher salt
- 150 g or ¾ c granulated sugar
- 339 g or 12 oz unsalted butter, cut into ½-in pieces, unsalted
- 339 g or 12 oz bittersweet chocolate, melted and cooled
- 6 g or 1 ½ tsp vanilla
Make the cake:
- Butter and flour three cake pans and line them with parchment. If using a good quality baking spray, apply it just before filling the pans. Preheat the oven to 350 F.
- In a medium bowl, whisk together the cocoa and boiling water until smooth. Cool to room temperature. Tip: Place the bowl over a pan filled with ice water and stir occasionally. Make sure the bowl is secure and doesn’t tip.
- In a medium bowl, beat the eggs lightly with ¼ of the cocoa mixture and the vanilla.
- In the bowl of a stand mixer fitted with the paddle attachment, mix the rest of the dry ingredients on low speed until combined. Add the butter and the rest of the cocoa mixture. Mix on low speed until the ingredients are combined (30 seconds). Add the butter and the remaining cocoa mixture. Increase the speed to medium and beat until the mixture is thoroughly combined (1 1/2 minutes). Scrape down the sides.
- Add the egg mixture in three batches, beating for 20 seconds after each addition. Then, scrape down the bowl once more.
- Divide the batter among the prepared cake pans and smooth the surface with an offset spatula. Bake until a toothpick inserted in the centre comes out clean and the cake springs back when lightly touched (25–30 minutes).
- Let the cakes cool in the pans for 10 minutes before removing them and letting them cool on wire racks.
Make the frosting:
- In the bowl of a stand mixer fitted with the whisk attachment, beat the eggs, egg yolks and salt until pale and thick (4 minutes).
- In a medium saucepan over medium-high heat, bring the sugar and 1/3 c of water to boil. Continue to cook, swirling occasionally (not stirring), until the temperature reaches 248°F (firm ball stage).
- With the mixer running, gradually pour the syrup into the egg mixture, where the eggs meet the sides of the bowl (avoid the beaters as much as possible, as they will cause the syrup to splash and thicken too quickly). Beat until the eggs are light and fluffy and the outside of the bowl is cool to the touch (5 minutes). Tip: hold a bag of frozen vegetables to the outside of the bowl to quickly bring the temperature down.
- One piece at a time, beat in the butter. Make sure each piece is incorporated before adding the next. Take your time with this. If the mixture begins to look soupy or curdled, just relax. It’ll come together. Just keep beating.
- Beat in the chocolate and vanilla.
*King Arthur Bakery Triple Cocoa Blend works well for recipes calling for both Dutch-process and regular cocoa. If you only want to keep track of one cocoa powder in your pantry, this is an excellent choice.
Cake adapted from Perfect All-American Chocolate Butter Cake, The Cake Bible by Rose Levy Berenbaum
Frosting adapted from Bon Appetit Chocolate Buttercream