Let’s construct this elegant Opera-inspired Cake! First, prepare the oven and baking sheet for the Joconde sponge. Preheat the oven to 425°F (220°C). Line a large baking sheet (e.g., half-sheet pan, 13×18 inches) smoothly with parchment paper, ensuring it lies flat. Set aside.

Make the simplified Joconde batter. In a large bowl, beat the room temperature eggs with the sifted powdered sugar using an electric mixer on high speed for several minutes, until the mixture is very thick, pale, significantly increased in volume, and forms a ribbon when the whisk is lifted.

In a separate bowl, whisk together the almond flour and the all-purpose flour. Gently fold this flour mixture into the whipped egg mixture in two or three additions using a large spatula, being careful not to deflate the eggs too much. Finally, gently fold in the melted and slightly cooled butter and the 2 tablespoons of Frangelico until just combined.

Pour the Joconde batter onto the prepared baking sheet. Using a large offset spatula, spread the batter quickly and evenly into a thin rectangle covering the entire sheet (or to the dimensions needed for your mould layers). Aim for a thickness of about 1/4 inch. Bake for 8-10 minutes, watching closely, until the sponge is lightly golden, set, and springs back when gently touched. Do not overbake, or it will become brittle.

Let the Joconde cool on the baking sheet for a few minutes, then carefully invert it onto another piece of parchment paper or a clean tea towel dusted with powdered sugar. Gently peel off the baking parchment. Let the sponge cool completely. Once cool, trim the edges and carefully cut the sponge into precise, identical rectangles based on the size of your assembly mould (typically three or four rectangles). Handle gently as it can be fragile.

Prepare the Coffee Soak: Brew strong coffee and let it cool, OR make a simple coffee syrup by boiling equal parts water and sugar with strong espresso powder until sugar dissolves, then let cool completely.

Make the Coffee Ganache: Finely chop the dark chocolate and place it in a heatproof bowl. Heat the heavy cream in a small saucepan just until simmering. Pour the hot cream over the chocolate. Let sit for 2-3 minutes, then whisk gently until completely smooth and glossy. Stir in the optional coffee liqueur. Let the ganache cool and thicken slightly at room temperature until it’s spreadable but not firm (like thick pudding).

Make the Simplified Coffee Buttercream: In a large bowl, beat the softened butter with an electric mixer until very pale and fluffy (3-5 minutes). Gradually beat in the sifted powdered sugar on low speed until incorporated. Add the completely cooled brewed coffee, vanilla extract (if using), and a pinch of salt. Increase speed to medium-high and beat for another 2-3 minutes until light, fluffy, and smooth.

Assemble the Opera Cake within your rectangular mould or frame placed on a flat platter or board lined with parchment/acetate. Place the first Joconde rectangle snugly inside the mould. Using a pastry brush, generously soak the layer evenly with the cooled coffee soak. Spread a thin, even layer of the Coffee Buttercream over the soaked sponge (an offset spatula is best).

Carefully place the second Joconde rectangle on top of the buttercream. Soak this layer evenly with the coffee soak. Spread a thin, even layer of the Coffee Ganache over this soaked layer.

Place the third Joconde rectangle on top. Soak this layer evenly with coffee soak. Spread another thin, even layer of Coffee Buttercream over this layer. (If using four layers, repeat soak/ganache or soak/buttercream as desired before adding the final layer). Place the final Joconde rectangle on top. Soak this top layer lightly.

Chill the assembled cake within the mould for at least 30-60 minutes to firm up the layers before glazing or finishing.

Prepare and apply the Chocolate Glaze (conceptual, as no recipe provided): Gently warm a mixture of finely chopped dark chocolate with a little butter or neutral oil until just melted and smooth. It should be very fluid. Pour the thin glaze over the chilled cake (still in the mould ideally, or remove mould carefully first) and quickly spread it into a very thin, even layer using a large offset spatula. Let the glaze set completely in the refrigerator (at least 1-2 hours).

Once fully set, carefully remove the mould/frame (warming the sides slightly with a hairdryer or warm towel can help release it cleanly). Trim the edges with a hot, sharp knife for perfectly neat sides if desired. Traditionally, “Opéra” is sometimes written on top with leftover buttercream or chocolate. Alternatively, finish simply with a dusting of cocoa powder if skipping the glaze. Slice carefully with a hot, sharp knife and serve chilled.