Gâteau Opéra

1.For almond joconde, preheat oven to 180C, and butter and line two 27cm x 37cm Swiss roll pans with baking paper. Whisk eggwhite, sugar and a pinch of salt in an electric mixer until firm peaks form (6-8 minutes), add eggs and whisk until pale and fluffy (3-4 minutes). Fold in almond meal, icing sugar and flour, then fold in butter and coffee. Spread mixture evenly between prepared pans, smooth tops and bake, swapping pans occasionally during cooking, until golden brown and cake springs back when lightly pressed (7-8 minutes). Turn out onto baking paper lightly dusted with flour, remove backing paper and set aside to cool (30 minutes).

2.For coffee buttercream, stir 200gm sugar and 80ml water in a small saucepan over medium-high heat until sugar dissolves, brush down sides of pan with a wet pastry brush, then bring to the boil and cook without stirring until syrup reaches 121C on a sugar thermometer (4-5 minutes). Meanwhile, whisk eggwhite and remaining sugar on high speed in an electric mixer until firm peaks form (4-5 minutes) then, when syrup reaches correct temperature, reduce speed to medium, gradually drizzle syrup in down sides of mixer bowl then whisk on high speed until fluffy and cooled to room temperature (4-5 minutes). Whisk in butter a little at a time until pale and fluffy (5-6 minutes), then whisk in coffee and set aside.

3.For ganache, bring cream, coffee and brandy to the simmer in a saucepan over medium-high heat, remove from heat, add chocolate, butter and a pinch of salt, stand for 5 minutes, then stir until smooth and combined. Reserve.

4.To assemble, lightly oil an 11cm x 27cm straight-sided 11cm-deep loaf tin, then line the base and sides with baking paper, leaving about 10cm of overhang at each long side (to lift the set cake from tin). Cut four 11cm x 27cm rectangles from joconde, and place one in the base of tin and brush with a little coffee. Spoon in enough coffee buttercream to form a 5mm-thick layer, spreading evenly (a small offset spatula is the best tool for this), then freeze until just firm (10 minutes). Pour over a thin layer of ganache, spreading evenly, top with another piece of joconde and repeat brushing, layering and freezing, until you use up the last layer of joconde (you may not need all the coffee buttercream). Brush with coffee, finish with a thin layer of ganache and refrigerate until firm (3-4 hours). Cake will keep covered and refrigerated for 1-2 days.

5.To serve, carefully lift cake from tin by overhanging paper, peel paper from sides, then trim sides with a hot, wet knife. Scatter with chocolate curls and slice using a hot, wet knife.