1. Make the Joconde Sponge:

Preheat oven to 425°F (220°C). Line a large baking sheet (approx. 12×17 inches or half-sheet size) with parchment paper. Do not grease.

In a large bowl (stand mixer with whisk attachment recommended), beat the room temperature eggs with the powdered sugar on medium-high speed until the mixture is very thick, pale, and ribbon-like (when you lift the whisk, the batter falls in a ribbon that stays visible for a few seconds), about 5-8 minutes.

Meanwhile, sift or process together the almond flour, all-purpose flour, (Self-correction: Original recipe adds confectioner’s sugar here, not granulated). Okay, confirming: almond flour + powdered sugar + AP flour + salt (if using). Whisk these dry ingredients together.

Gently fold the dry ingredients into the whipped egg/sugar mixture in additions, being careful not to deflate the volume too much.

Gently fold in the melted and slightly cooled butter until just combined. Do not overmix.

Spread the Joconde batter very thinly and evenly over the prepared parchment-lined baking sheet using a large offset spatula.

Bake for 8-10 minutes, until lightly golden and just set (springs back when lightly touched). Watch carefully – it bakes quickly!

Let cool slightly on the baking sheet, then carefully invert onto another piece of parchment or a clean towel. Peel off the baking parchment. Let cool completely. Once cool, trim edges and cut into 3 or 4 equal rectangles (depending on desired height/assembly method).

2. Make the Coffee Syrup:

While the Joconde cools, place espresso powder, sugar, and water into a saucepan.

Bring to a boil, stirring until sugar dissolves. Remove from heat and let cool completely.

3. Make the Coffee Ganache:

Place chopped dark chocolate in a heatproof bowl.

Heat heavy cream in a small saucepan or microwave until just simmering.

Pour hot cream over the chocolate. Let sit for 2-5 minutes.

Whisk gently until completely smooth and glossy. Stir in coffee liqueur, if using. Let cool to a thick but spreadable consistency (room temp or slightly chilled).

4. Make the Coffee Buttercream:

In a large bowl (stand mixer with paddle attachment preferred), beat the softened butter until very smooth and creamy.

Gradually add the sifted powdered sugar, beating on low speed until incorporated, then medium speed until smooth. Add salt and vanilla if using.

Slowly beat in the cooled brewed coffee until the frosting is light, fluffy, and spreadable. Adjust consistency with more sugar (if too thin) or a tiny bit more cool coffee/milk (if too stiff).

5. Assemble the Opera Cake (Mold Recommended):

If using a rectangular cake mold or frame lined with acetate, place it on your serving platter. If assembling freehand, work carefully.

Place the first layer of Joconde sponge inside the mold (or on the platter).

Brush the sponge generously with the cooled coffee syrup using a pastry brush.

Spread a thin, even layer of the coffee ganache over the soaked sponge. Chill briefly (10-15 mins) if needed for firmness.

Place the second layer of Joconde sponge on top. Brush generously with coffee syrup.

Spread a thin, even layer of the coffee buttercream over the soaked sponge. Chill briefly if needed.

Place the third layer of Joconde sponge on top. Brush generously with coffee syrup. (Add a fourth layer repeating ganache or buttercream if desired and your layers are thin enough).

Apply a very thin layer of buttercream over the top layer (and sides if assembling freehand) as a crumb coat. Chill the assembled cake thoroughly, at least 1-2 hours, until firm.

6. Glaze and Finish:

Prepare your chocolate glaze according to its recipe (typically heating chocolate, butter, corn syrup, water). Let it cool slightly until it’s fluid but not hot.

Pour the glaze over the chilled, firm cake, allowing it to coat the top smoothly and drip down the sides (if assembled freehand) or fill the top neatly within the mold. Use an offset spatula to smooth the top quickly if needed.

Chill the cake again until the glaze is set, at least 30 minutes.

Carefully remove the cake from the mold/frame if used. Trim edges with a hot, sharp knife for very neat presentation if desired.

Dust the top lightly with cocoa powder. You can also traditionally write “Opéra” in melted chocolate or carefully score the glaze.

7. Serve:

Let the cake sit at room temperature for about 20-30 minutes before serving for the best texture. Slice into small, neat rectangles or squares using a hot, clean knife. Enjoy!