OpéraOpéra Cake

Make the biscuit Joconde batter

• 1 Melt 20g unsalted butter in a small saucepan, let stand briefly and reserve only the clear upper portion as clarified butter.
• 2 Beat 4 whole eggs, 100g almond flour and 100g powdered sugar in a bowl with a hand mixer until pale and doubled in volume.
• 3 In another bowl, add 0.5g salt to 3 whites and beat to firm peaks.
• 4 Sift 28g cake flour into the egg batter and fold with a flexible spatula, mix in the clarified butter, then add to the beaten whites and combine without deflating.
• 5 MeanwhileWhile beating, preheat the oven to 180°C and line a 27cm square baking sheet with parchment.

Spread thinly in a 27cm square and bake at 180°C for 12 minutes, twice

• 1 Spread half the batter flat on the baking sheet about 5mm thick and bake at 180°C for 12 minutes.
• 2 Transfer with its paper to a rack to cool. Bake the remaining batter in the same way.

Make and cool a strong coffee syrup

• 1 Heat 100ml water and 60g sugar in a small saucepan over medium heat. When the sugar dissolves, turn off the heat, dissolve 6g instant coffee in it and cool.

Whip yolks with 121°C syrup and add butter and coffee

• 1 Beat 3 yolks in a bowl with a hand mixer until pale.
• 2 Heat 30ml water and 90g sugar in a small saucepan and cook to 121°C, checking with a thermometer.
• 3 While beating the yolks, pour the hot syrup in a thin stream down the bowl edge and beat until cool to make pâte à bombe, yolks whipped with hot syrup.
• 4 Gradually add 90g softened unsalted butter while beating, then mix in 2g instant coffee dissolved in 1 teaspoon hot water to make crème au beurre, or buttercream.

Make ganache and chill until spreadable

• 1 Finely chop 120g couverture chocolate and put in a bowl.
• 2 Heat 76ml cream to just below boiling and pour over. Leave for 1 minute, stir from the center to melt, then mix in 30g unsalted butter to make ganache, chocolate combined with heated cream.
• 3 Refrigerate, stirring every 5 minutes. When creamy, take out to room temperature.

Cut 18cm squares, coat the bottom with chocolate and layer in a frame

• 1 Cut 2 squares of 18cm from the cooled sponge and combine the scraps to make a third 18cm square.
• 2 Melt 40g chocolate over a water bath, spread thinly on one side of 1 intact square and refrigerate for 10 minutes to set.
• 3 Set an 18cm square frame on a parchment-lined work surface. Put the chocolate-coated sponge inside, chocolate side down. Brush generously with coffee syrup and spread half the buttercream, about 120g, in a level layer 3–4mm thick.
• 4 Brush one side of sponge sheet 2, made from scraps, with syrup and place syrup side down. Brush the top too and spread the ganache thinly and evenly.
• 5 Brush both sides of sheet 3 with syrup in the same way, place on top and level the remaining buttercream to 3–4mm thick.

Refrigerate for at least 2 hours

• 1 Refrigerate in the frame for at least 2 hours.

Unmold and spread a thin chocolate glaze in one stroke

• 1 Wrap the outside of the frame in a warmed cloth to release it, remove and place the cake on a rack over a tray.
• 2 Melt 160g chocolate over a water bath, mix in 24g grapeseed oil and cool until warm to the touch.
• 3 Pour over the cold cake and spread thinly from edge to edge in one stroke with an offset spatula, letting excess run down. Refrigerate for 10 minutes.

Trim the edges, write “Opéra” and add gold leaf

• 1 Warm a knife in hot water, wipe dry and trim 0.5cm from all four sides.
• 2 Melt 10g chocolate over a water bath, transfer to a parchment cornet and write “Opéra” on top. Optionally add 1 small piece of edible gold leaf.
• 3 Cut into 9 portions, warming and wiping the knife as you go, and refrigerate.