Cuban Opera Cake

Description
This cake can be made a day ahead of time and kept refrigerated. Just allow to stand at room temperature for an hour before serving.

Cake

 * 4 ounces bittersweet or semisweet chocolate, chopped
 * 2 cups all-purpose flour
 * 2 teaspoons baking soda
 * ½ teaspoon salt
 * 2 cups light brown sugar (packed)
 * ½ cup unsalted butter, room temperature
 * 3½ teaspoons vanilla extract
 * 4 large eggs
 * 1 cup sour cream
 * ½ cup crème de cacao
 * ½ cup freshly brewed coffee, lukewarm

Buttercream

 * 8 ounces milk chocolate, chopped
 * ½ cup sugar
 * 4 large egg yolks
 * 2 tablespoons water
 * 2 tablespoons light corn syrup
 * ¾ cup unsalted butter, room temperature

Coffee mousse

 * ½ cup half and half
 * 4 tablespoons sugar
 * 1 tablespoon instant espresso or coffee powder
 * 4 large egg yolks
 * 1 teaspoon unflavored gelatin softened in 1 tablespoon water 10 minutes
 * 1 cup chilled whipping cream
 * 1 teaspoon vanilla extract

Chocolate glaze

 * 1½ cups sugar
 * 1 cup water
 * ½ cup unsweetened cocoa powder
 * 12 ounces bittersweet or semisweet chocolate, chopped

Cake

 * 1) Preheat oven to 325°F.
 * 2) Butter two 9" diameter cake pans with 2" high sides; line bottoms with parchment paper rounds.
 * 3) Dust pans with flour; tapping out any excess flour.
 * 4) Melt chocolate in the top of a double boiler over simmering water, stirring until melted and smooth.
 * 5) Remove the top part of the double boiler and allow the mixture to cool until it is lukewarm.
 * 6) Whisk flour, baking soda, and salt together in a medium-sized bowl.
 * 7) Using an electric mixer, beat the sugar, butter, and vanilla in large bowl.
 * 8) Add the eggs one at a time, beating well after each addition and stopping occasionally to scrape down sides of bowl.
 * 9) Gradually beat in the lukewarm melted chocolate.
 * 10) Beat in the dry ingredients using one third of the ingredients at a time alternately with half the sour cream, beginning and ending with dry ingredients.
 * 11) Gradually beat in the crème de cacao and coffee.
 * 12) Divide batter evenly between the two pans and smooth out the tops.
 * 13) Bake until a toothpick inserted into the center of each comes out clean (about 35 minutes).
 * 14) Cool cakes in pans on racks 10 minutes.
 * 15) Invert cakes onto 9-inch cardboard rounds or removable tart pan bottoms and allow them to cool completely on racks.

Buttercream

 * 1) Melt milk chocolate in top of a double boiler over simmering water, stirring until smooth.
 * 2) Set the top portion of the double boiler aside to the allow the chocolate to cool.
 * 3) Whisk the sugar, egg yolks, 2 tablespoons of water, and the corn syrup in medium-sized metal bowl to blend.
 * 4) Add ¼ cup of butter.
 * 5) Set the bowl over the saucepan of simmering water and whisk constantly until the mixture reaches 170°F (about 4 minutes).
 * 6) Remove the bowl and set aside.
 * 7) Using an electric mixer, beat the mixture until it is completely cool and thick (about 6 minutes).
 * 8) Gradually beat in ½ cup butter a bit at a time, mixing thoroughly before adding the next bit and stopping occasionally to scrape down sides of bowl.
 * 9) Beat in the lukewarm melted chocolate.

Coffee mousse

 * 1) Bring the cream, 2 tablespoons sugar and espresso powder to a simmer in a small saucepan on medium-high heat.
 * 2) Whisk egg yolks and remaining 2 tablespoons sugar together in a medium bowl.
 * 3) Gradually whisk in  the hot cream mixture into yolk mixture.
 * 4) Return the mixture to the saucepan and stir constantly over medium heat until thermometer registers 160°F (about 2 minutes).
 * 5) Pour into a large bowl.
 * 6) Add the softened gelatin, stirring until it is completely dissolved.
 * 7) Using an electric mixer, beat the mixture until it is cool (about 10 minutes).
 * 8) Using clean, dry beaters, beat cream and vanilla in medium bowl until stiff peaks form.
 * 9) Fold the whipped cream into the coffee mixture.

Assembly

 * 1) Cut both cake layers horizontally in half.
 * 2) Place 1 cake layer in bottom of 9-inch-diameter spring-form pan.
 * 3) Cover with ¾ cup the buttercream.
 * 4) Place a second cake layer  on top of the buttercream layer and cover with mousse.
 * 5) Top with a third cake layer.
 * 6) Refrigerate 1 hour to allow the mousse to set.
 * 7) Remove from the refrigerator and spread ¾ cup of buttercream over third cake layer.
 * 8) Top with a fourth cake layer (don't worry, the cake now be taller than the sides of the pan).
 * 9) Cover and refrigerate at least 4 hours, preferably overnight.

Chocolate glaze

 * 1) Stir sugar and 1 cup water in medium saucepan over medium heat until the sugar dissolves.
 * 2) Increase the heat to high and bring to a boil.
 * 3) Whisk in the cocoa then remove from heat.
 * 4) Add the chocolate and whisk the mixture until it is smooth.
 * 5) Let stand until cool but still pourable (about 2 hours).
 * 6) Run knife around sides of the pan to loosen the cake, then release pan sides.
 * 7) Scrape any excess mousse from sides of cake.
 * 8) Transfer cake (still on the spring-form pan bottom) to a rack set over a baking sheet or other shallow pan.
 * 9) Pour the glaze over the cake, allowing it to drip down edges onto baking sheet (use spatula to spread glaze over any uncovered spots).
 * 10) Refrigerate at least 2 hours to allow glaze to set.