- Prep time 1 hour 45 minutes
- Cook time 55 minutes
- makes 1 (8-inch) cake
Making an opera cake is not for the faint of heart, so this is not a recipe to make when you only have about 30 minutes to put it together. The classic French cake is a six-layer masterpiece featuring tender joconde sponge cake, a rich chocolate ganache, and a smooth coffee buttercream. Although there are many components to this cake, it’s a joy to eat and an impressive dessert to make for a special occasion. You just won't be able to get over all those pretty layers! I’ve done my best to make this cake as straightforward as can be, but there’s no getting around it: For a stellar opera cake, you will have to set aside a few hours of your time (perhaps an afternoon) to make it from start to finish.
I find it more enjoyable to break it up in parts: The ganache, buttercream, and coffee soak can all be made ahead of time, and both the ganache and coffee soak are fairly straightforward. Once you bake your cake on the day of, assembling it takes no time at all. It is essential that the butter for your ganache and buttercream are room temperature. Buttercreams are prone to splitting, and having your ingredients at the right temperature will help reduce the risk of that. A joy of a project, you'll love the end result. Let us know how yours turns out! —Genevieve Yam
(½ cup plus 2 teaspoons) all-purpose flour, divided, plus more for the pan
(1 cup and 2 tablespoons) granulated sugar, divided
(¾ cup) blanched almond flour
(2 teaspoons) baking powder
(½ teaspoons) kosher salt
(150 grams) large eggs
stick (8 tablespoons) unsalted butter, melted
large egg whites (from about 3 large eggs)
egg whites (a little fewer than 3), room temperature
plus 40 grams (¾ cup plus ⅓ cup) granulated sugar, divided
(3 tablespoons plus 1 teaspoon) water
(2 sticks plus 3 tablespoons) unsalted butter, room temperature
(1½ teaspoons) coffee extract
(227 grams) semisweet or bittersweet chocolate, finely chopped
(240 milliliters) plus 2 tablespoons heavy cream
stick (57 grams) unsalted butter, room temperature and cut into 4 pieces
- Bake the Cake: Heat the oven to 175ºC/350ºF. Grease and flour an 8-inch cake pan, then line the bottom with parchment paper.
- In a large bowl, whisk 113 grams (½ cup) of the sugar, the almond flour, ½ cup of the all-purpose flour, the baking powder, and salt. Add the whole eggs and melted butter and whisk until smooth.
- Check to see that the bowl of your stand mixer is clean and dry. Place the egg whites in the bowl, then beat with the whisk attachment on medium speed. When foamy, slowly stream in the remaining 113 grams of the sugar. Increase the speed to medium-high and whisk for 4 to 5 minutes, until stiff peaks form.
- Using a rubber spatula, gently fold one-third of the egg whites into the batter. Add the remaining egg whites and gently fold—being careful to not deflate the egg whites—until no streaks remain.
- Pour the batter into the prepared pan. Bake for 35 to 45 minutes, until the cake is lightly browned and begins to pull away from the pan. Press gently; it should spring back.
- Let cool in the pan for 15 minutes. Gently run an offset spatula around the pan, then invert onto a wire rack. Remove the parchment and let cool completely. Slice the cake evenly into 3 layers horizontally.
- Make the Coffee Soak: In a small saucepan over medium heat, bring the sugar and coffee to a simmer, stirring to dissolve the sugar. Remove from the heat and pour into a heatproof container. Alternatively, place the coffee and sugar in a microwave-safe bowl and microwave for 30 seconds, until the sugar has dissolved.
- Make the Buttercream: Place the egg whites in a clean, dry bowl of a stand mixer and beat with the whisk attachment on medium-low speed. When foamy, slowly rain in 40 grams (⅓ cup) of the sugar, then whisk until very soft peaks form. Reduce the speed to the lowest speed.
- In a small saucepan over high heat, cook 180 grams (¾ cup) of the sugar and the water, not stirring, until an instant-thermometer registers 115ºC/240ºF. Remove from the heat.
- Increase the speed of the mixer to medium-high, then slowly and carefully pour the hot sugar syrup down the side of the bowl. Whip until cool. This can take up to 15 or 20 minutes, but is essential so the butter doesn’t melt when you begin to incorporate it.
- Once the egg whites are cool (they should be at stiff peaks and glossy), press the butter between your fingers (helps for easier emulsifying!) and add a few pieces at a time. Slowly add the rest of the butter—do not add it all at once, or your buttercream will break—then add the coffee extract and salt. It should be thick and creamy. If the buttercream is loose or runny, place the bowl in the fridge for a few minutes to help cool it down, then continue whisking in the stand mixer until thick.
- Fill an uncut piping bag with the coffee buttercream and set aside.
- Note: To fix a broken buttercream, place it in the bowl of a stand mixer with the whisk attachment and whisk until emulsified. If it is too cold, warm it up slightly with a warm, wet towel wrapped around the bowl or place the bowl on top of a double boiler until it’s warmed up ever so slightly.
- Make the Chocolate Ganache: Place the chopped chocolate in a medium heatproof bowl.
- Bring the cream to a boil (you can do this in a microwave oven) and pour half over the chocolate. Wait for 30 seconds. Using a whisk or a heatproof spatula, gently stir the chocolate and cream together in small circles, starting in the center of the bowl and working your way out in ever-widening concentric circles. Pour in the rest of the cream and repeat the circular mixing. When the ganache is smooth and shiny, drop in the butter pieces one by one, mixing until each piece is blended before adding the next. Be gentle—you don’t want to beat the ganache, nor do you want to aerate it.
- Let the ganache cool at room temperature until thickened and spreadable. Fill an uncut piping bag with ½ cup of the ganache; set the remaining aside for glazing the cake. If making ahead, cover the top of the ganache with plastic wrap to prevent a skin from forming and let it sit at room temperature.
- Finally, Assemble!: Place the first layer of the cake on an 8-inch cake board, then place it atop a wide plate or a turntable. Using a pastry brush, soak the cake generously with the coffee soak. Pipe a circle of buttercream, around 1 centimeter tall, along the edges of the cake to form a border, then fill it by piping an even layer of buttercream. Use an offset spatula to smooth it out.
- Gently but firmly press the second layer of cake onto the buttercream; brush with the coffee soak. Just as you did with the buttercream, pipe a circle of ganache along the edges of the cake to form a border, then pipe to fill with the ganache. Smooth it out with an offset spatula.
- Press the final layer of cake onto the ganache, then repeat the buttercream piping. Smooth it out with an offset spatula, then refrigerate the cake until the buttercream is chilled and set, about 30 minutes.
- Gently reheat the remaining chocolate ganache until it is liquid enough to pour over the cake as a glaze. When the buttercream has set, remove the cake from the fridge and place it on a cooling rack set above a sheet tray. Pour the ganache on top of the buttercream, and spread evenly using an offset spatula. Return the cake to the fridge and allow to chill until the ganache has set. Once chilled, remove the cake from the fridge and use a warm, clean knife to slice the sides off to create a square cake, and portion as desired.