Prepare pans and oven: Heat oven to 425°F (220°C). Line a half-sheet pan with parchment and lightly grease. If using two pans, divide batter between them.

Make the Joconde base: In a bowl, whisk almond flour, powdered sugar, and all-purpose flour. Add whole eggs and whisk until thick and pale, 2–3 minutes. Stir in melted butter and salt.

Whip egg whites: In a clean bowl, whip egg whites to soft peaks. Gradually add granulated sugar and whip to glossy medium peaks. Fold gently into the almond mixture in two additions.

Bake the sponge: Spread batter in an even, thin layer. Bake 7–10 minutes until lightly golden and springy. Do not overbake. Cool completely, then loosen edges and flip onto a fresh parchment sheet. Peel away the baking parchment.

Make the coffee syrup: Warm coffee and sugar in a small saucepan until dissolved. Remove from heat, add vanilla and optional liqueur, and cool.

Make coffee French buttercream: Put yolks in a mixer bowl with whisk attachment. In a small saucepan, heat sugar and water to 238°F (114°C) without stirring. Start whisking yolks on medium, then slowly stream the hot syrup down the side of the bowl. Whip until the bowl is just warm and mixture is thick, 4–6 minutes. Add butter a few cubes at a time until silky. Mix in espresso concentrate and a pinch of salt. If it looks broken, keep mixing; it usually comes together.

Make the ganache: Heat cream to a simmer, pour over chopped chocolate, and let sit 1–2 minutes. Stir until smooth. Add butter and salt. Cool until spreadable but not firm.

Trim and portion the sponge: Trim the edges for clean lines. Cut the sponge into three equal rectangles (or two if you prefer a shorter stack). Aim for uniform thickness.

Assemble the layers: Place the first sponge on a board, smooth side up. Brush generously with coffee syrup; it should be moist but not soggy.

Spread a thin, even layer of coffee buttercream.

Top with the second sponge. Brush with syrup. Spread an even layer of ganache.

Add the third sponge. Brush with syrup. Finish with a thin layer of buttercream to smooth the surface.

Chill to set: Refrigerate the assembled cake for 45–60 minutes until firm to the touch. This helps with a clean glaze and neat cuts.

Glaze: Melt chocolate with oil (or cocoa butter) gently until smooth and fluid. Let it cool to about 90–92°F (32–33°C) so it’s pourable but not hot. Pour over the chilled cake and spread quickly with an offset spatula for a thin, shiny layer.

Final chill and trim: Chill 20–30 minutes until the glaze is set but not rock hard. Use a hot knife (warmed and wiped dry) to trim edges for sharp sides. Slice into neat rectangles.