For the Cake
- 2 2/ 3 cups cake flour
- 2 teaspoons baking powder
- 1/ 2 teaspoon fine sea salt
- 1 cup vegetable oil
- 3/ 4 cup whole milk, at room temperature
- 1 tablespoon vanilla extract
- 8 large eggs, at room temperature
- 2 1/ 3 cups granulated sugar
For the Dark Chocolate Italian Buttercream
- 4 large egg whites
- 1 3/ 4 cups granulated sugar
- 1/ 3 cup water
- 1 pound unsalted butter, at room temperature
- 2 teaspoons vanilla extract
- 1 pound dark chocolate, coarsely chopped, melted, and cooled slightly
- Flaked sea salt, for sprinkling (optional)
Preheat the oven to 350°F, with a rack in the middle. Grease and flour two 8-inch round cake pans.
Make the cakes: Sift the cake flour, baking powder, and salt together into a medium bowl. In a container with a spout (such as a 2 cup liquid measure), whisk together the oil, milk, and vanilla.
In the bowl of a stand mixer fitted with the whisk attachment (or in a large heatproof bowl, using a hand mixer), be at the eggs and sugar to combine. Set the bowl over a medium saucepan of barely simmering water (with the bowl not touching the water) and heat, whisking constantly, until the mixture registers 105°F on an instant read thermometer.
Remove the bowl from the saucepan and whip the mixture on high speed until pale and thick, 5 to 6 minutes. Reduce the speed to medium and beat for 2 to 3 minutes more (this will help stabilize the foam).
Sprinkle about one quarter of the flour mixture over the egg mixture and mix on low speed just until incorporated. Add the remaining flour mixture in 2 to 3 additions, mixing just until incorporated into the batter. Gradually drizzle the milk mixture into the batter, mixing just until incorporated.
Divide the batter between the prepared pans (about 730 g per pan). Bake the cakes until the centers spring back when touched, 45 to 55 minutes. Cool in the pans for 15 minutes, then invert onto a wire rack to cool completely.
Make the buttercream: Place the egg whites in the bowl of a stand mixer fitted with the whisk attachment (or use a large bowl and a hand mixer).
In a medium saucepan, combine the sugar and water and bring to a boil over medium heat, stirring constantly to help dissolve the sugar. Once the mixture comes to a boil, stop stirring (if any sugar clings to the sides, use a pastry brush dipped in cool water to brush it back down into the syrup). Attach a candy thermometer to the side of the saucepan (or have an instant read thermometer at the ready).
When the syrup reaches 235°F, begin whipping the egg whites on medium high speed. (The goal is to get the whites to soft peaks by the time the sugar reaches 240°F.)
When the whites are at soft peaks and the syrup has reached 240°F, with the mixer running, pour the syrup into the whites in a slow, steady stream. Then continue whipping on medium high until the meringue is firm, glossy, and cool and the bowl is no longer warm to the touch, 5 to 6 minutes.
With the mixer running on medium speed, gradually add the butter, 1 to 2 tablespoons at a time, to the meringue, waiting until each addition is incorporated before adding more. Add the melted chocolate and mix to combine. Set aside.
Assemble the cake: Use a serrated knife to level the top of each cake and then cut each one into two layers.
Place one layer on a turntable or cake stand (or a platter). Scoop ½ cup of the buttercream onto the layer and use an offset spatula to spread it evenly. Repeat with 2 more layers and more buttercream. Top the cake with the fourth layer. Apply a crumb coat of buttercream to the top and sides of the cake and refrigerate to set, 15 to 30 minutes.
Frost the sides and top of the cake. Refrigerate the cake for at least 15 minutes before slicing (it will slice more cleanly this way).
Slice the cake and sprinkle each slice with a little flaky sea salt, if desired.
BASIC YELLOW SPONGE CAKE WITH DARK CHOCOLATE ITALIAN BUTTERCREAM is excerpted from THE FEARLESS BAKER © 2017 by Erin Jeanne McDowell. Reproduced by permission of Rux Martin/ Houghton Mifflin Harcourt. All rights reserved.
WHY IT WORKS:
For this basic sponge cake, the key is to achieve full volume when beating the eggs and then deflate them as little as possible when adding the remaining ingredients. As the cake bakes, the air incorporated expands so the cake rises. In this cake, the addition of baking powder helps make the cake extra light and rise even higher and more evenly. For the Italian meringue, adding a hot sugar syrup to beaten eggwhites and continuing to beat them allows you to achieve up to eight times their original volume.
It’s especially important not to overmix a sponge cake batter you’ll lose the volume created by aerating the eggs and end up with a dense, flat disk. But it’s also important to make sure the flour is fully incorporated, because you don’t want “flour bombs” pockets of flour that don’t get mixed in. If you’re unsure, mix the flour in by hand, adding it a little at a time and folding it in gently with a silicone spatula until incorporated