French Opera Cake

Step 1

Preheat the oven to 425°F. Butter a 12x17-inch rimmed sheet pan and line it with parchment paper.

Step 2

In a large bowl, whisk 4 whole eggs with the almond flour and 1/2 cup of the sugar until pale, thick, and doubled in volume, about 3 minutes.

Step 3

Sift the flour over the almond mixture and fold in gently, then melt 3 tablespoons of the butter and fold it in until smooth.

Step 4

Separate the remaining 2 eggs; in a clean bowl, whip the 2 egg whites with 2 tablespoons of the sugar to soft peaks (reserve the 2 yolks for the buttercream), then fold into the batter in two additions until no streaks remain.

Step 5

Spread the batter evenly across the prepared pan and bake for 8-10 minutes, until springy to the touch and lightly golden at the edges. Cool completely, then trim the edges and cut into three equal rectangles.

Step 6

For the coffee syrup, combine 1/4 cup of the coffee with 2 tablespoons of the sugar in a small saucepan and simmer 1 minute; set aside to cool.

Step 7

For the buttercream, whisk the reserved 2 egg yolks with 2 tablespoons of the sugar over a double boiler until pale and slightly thickened, about 3 minutes, then remove from heat; remove from heat and cool to room temperature, about 15-20 minutes (or stir over an ice bath for 3-4 minutes) — warm custard will melt the butter instead of whipping into buttercream.

Step 8

Beat 7 tablespoons of the softened butter into the cooled yolk mixture along with 2 tablespoons of the coffee until light and fluffy.

Step 9

For the ganache, heat 1/2 cup of the heavy cream just to a simmer, pour over the chopped dark chocolate, and let sit 2 minutes before stirring until smooth and glossy; cool until spreadable, about 15 minutes.

Step 10

Place one cake rectangle on a serving platter and brush generously with half of the coffee syrup.

Step 11

Spread half of the coffee buttercream evenly over the layer, then top with the second cake rectangle and brush with the remaining syrup.

Step 12

Spread the remaining buttercream over the second layer, then top with the final cake rectangle.

Step 13

Pour the ganache over the top layer and spread into a thin, even glaze, letting any excess drip down the sides.

Step 14

Chill the assembled cake at least 1 hour to set before trimming the edges for clean lines and slicing.

Step 15

Whip the remaining 1/2 cup heavy cream to soft peaks and serve alongside each slice, if desired.