I first saw a version this recipe in my big, yellow Gourmet cookbook that was published in 2004.  I love the taste of chocolate and orange together and thought this would be perfect for book club.  I have adapted the recipe after making this cake a few times.  First, I use a different cake recipe that I have baked many times with success.  That recipe is from my go-to America’s Test Kitchen and I’ve posted the recipe before with my Black Forest Cake.  Second, I eased back on the butter in the buttercream recipe.  Their version uses 6 1/2 sticks of butter.  I am definitely not butter-adverse, but the frosting came out a little too buttery if that’s possible!  My version is lighter without sacrificing the decadence.  Finally, I finished with candied orange slices.  Not necessary, but so pretty.  Recipe at bottom of post.

A few tips I’ve learned from making this cake.  First, this cake is a big undertaking with many components so it’s best to plan and make the cake in stages.  I bake and wrap the cake layers two days prior, make and refrigerate the ganache (a day ahead) and buttercream (one week ahead).  Rewhip the buttercream upon assembly.  Second, the buttercream and frosting of the cake should be made on a cool day.  I usually make this cake in the winter.  Finally, serve the cake at room temperature for the best taste and texture.

Special equipment needed:

Three 9″ round cake pans

Stand mixer

Candy thermometer

A pastry bag fitted with a 1/4-inch plain tip

For cake layers:
1/2 cup (1 1/2 oz) Dutch-processed cocoa powder, plus extra for dusting
1 1/2 cups (7 1/2 oz) all-purpose flour
1 tsp baking soda
1/2 tsp baking powder
1/4 tsp salt
1 1/4 cups boiling water
4 ounces unsweetened chocolate, chopped
1 tsp instant espresso or instant coffee
10 tbsp. (1 1/4 sticks) unsalted butter, softened
1 1/2 cups (10 1/2 oz) packed light brown sugar
3 large eggs, room temperature
1/2 (4 oz) cup sour cream, room temperature
1 tsp vanilla extract

Method:
1. Adjust the oven racks to the upper-middle and lower-middle position and heat the oven to 350 degrees. Grease 3 9-inch round cake pans, then dust with cocoa powder and line the bottoms with parchment paper. Dusting with cocoa powder, not flour, with chocolate cakes ensures there is no white flour all over baked cakes.  Whisk the flour, baking soda, baking powder, and salt together in a large bowl. In a medium bowl, whisk the boiling water, chocolate, 1/2 cup of the cocoa powder, and instant espresso together until smooth.
2. In a large bowl, beat the butter and sugar together with an electric mixer on medium speed until light and fluffy, 3-6 minutes. Beat in the eggs, one at a time, until combined, about 30 seconds. Beat in the sour cream and vanilla until incorporated.
3. Reduced the speed to low and beat in 1/3 of the flour mixture, followed by 1/2 of the chocolate mixture. Repeat with half of the remaining flour mixture and the remaining chocolate mixture. Beat in the remaining flour mixture until just incorporated.
4. Give the batter the final stir with a rubber spatula to make sure it is thoroughly combined. Scrape the batter into the prepared pans, smooth the tops, and gently tap the pans on the counter to settle the batter. Bake the cakes until a toothpick inserted in the center comes out with a few crumbs attached, 15-20 minutes, rotating and switching the pans halfway thorough baking.
5. Let the cakes cool in the pans for 10 minutes. Run a small knife around the edge of the cakes, then flip them out onto the wire racks. Peel off parchment paper, flip the cakes side up, let cool completely before frosting, about 2 hours.

For Ganache:

8 oz good bittersweet chocolate, finely chopped

2 tbsp. unsalted butter, softened

2 tsp finely grated orange zest

1 cup (8 oz) heavy cream

Method:  Place chocolate, butter, and zest in medium bowl.  Bring cream just to a bowl in small saucepan, then immediately pour into the bowl and let stand 5 minutes.  Whisky until chocolate is melted and smooth.  Refrigerate just until cool, about 25 minutes.

For Orange Buttercream Frosting:

Orange curd:

5 large egg yolds

1/4 cup (1 3/4 oz) sugar

2 tbsp. finely grated orange zest

1/2 cup (4 oz) fresh orange juice

1/2 stick (4 tbsp.) unsalted butter, softened

pinch of salt

1 1/2 tsp fresh lemon juice

Buttercream:

1 1/4 cup (8  3/4 oz)  sugar

1/2 cup (4 oz) water

5 large egg whites

1/2 tsp salt, plus a pinch

1/2 tsp cream of tartar

5 1/2 sticks of butter, cut into tablespoons and softened

Method:

Curd: Whisk together yolks and sugar in a small saucepan, then whisk in zest, orange juice, butter, and salt.  Cook over low heat, whisking constantly, until mixture just reaches boiling point, about 5 minutes.  Pour through a fine mesh colander into a bowl, pressing on solids. Discard solids.  Whisk in lemon juice.  Cover surface with plastic wrap and refrigerate at least one hour or up to two days.

Buttercream: Bring sugar and water to a boil in a small saucepan over moderately high heat, stirring and washing down any sugar crystals on the sides of the pan.  Boil syrup, without stirring, until candy thermometer registers 248 degrees.

Meanwhile, beat whites with a pinch of salt in bowl of mixer until foamy, then beat in cream of tartar.  Beat until whites just hold stiff peaks.

Slwoly add hot syrup, being careful to avoid beaters and sides of bowl, beating constantly at medium speed, and continute to beat until cool, 15-20 minutes.  (You must cool meringue completely before the next step).

Add butter, one piece at a time, still beating at medium speed until buttercream is thick and smooth.  Beat in curd and remaining 1/2 tsp salt.  Buttercream can be made up to one week ahead and refrigerated in an airtight container or froze for one month.  Bring to room temperature and beat with a mixer until smooth before using.

Candied Orange Slices (optional décor):

Thinly slice one or two oranges and remove seeds.  Bring to boil a mixture of 1:1 sugar and water.  Add orange slices and simmer about 45 minutes.  Remove slices, place on drying rack, and allow to dry completely overnight.  Sprinkle dried oranges with sugar.

Assembly:

Beat ganache with clean beaters just until light and fluffy.  Do not overbeat.  Reserve 2 cups of buttercream for decorating and piping.  Put one cake layer on stand and spread top evenly with half of ganache.  Cover with another layer and spread top with remaining ganache.  Cover with remaining cake layer and frost top and sides of cake smoothly with a very thin layer of buttercream (crumb coat).  Refrigerate cake, uncovered, for 30 minutes.

Generously frost top and sides of cake with remaining buttercream.  I like to make big swirly patterns with this frosting.  Refrigerate, uncovered, for about 30 minutes.  Finish by piping a decorative border with reserved buttercream and top with candied orange slices, if desired.

Refrigerate cake, covered, for up to one day.  Bring to room temperature (2-4 hours) before serving.