Opera — almond cake with coffee buttercream and chocolate

Prepare a baking sheet with internal dimensions of about 40 × 30 cm and line it with parchment paper. Preheat the oven to 200°C with conventional top and bottom heat. Beat the three whole eggs, ground almonds and confectioners' sugar with an electric mixer for about 5–6 minutes, until pale and distinctly fluffy. In a separate clean bowl, beat the three additional whites, adding the 20 g sugar, until glossy with a flexible peak. Gently fold the sifted flour into the almond mixture, then fold in the whites in two additions. Mix two tablespoons of batter into the melted butter, which should no longer be hot, then carefully fold this into the rest.

Spread all the batter in an even, thin layer on the prepared sheet, carefully leveling the corners too. Bake for about 10–12 minutes, until the surface is lightly golden and the center springs back; do not dry out the sponge. Remove from the oven, leave for 5 minutes, turn onto a clean sheet of parchment and carefully peel off the baking paper. Cool for about 20–30 minutes. Cut into three rectangles as evenly as possible, each about 13 × 30 cm. Set narrow uneven trimmings aside outside the servings. Trim the final straight edges only once the whole assembled cake is chilled.

Heat the 100 g water with 60 g sugar just until dissolved and briefly boiling. Take off the heat, dissolve the 4 g coffee in the liquid and set aside to cool, without reducing it for long. Measure out about 135 g finished coffee syrup for the cake and reserve the rest separately. For the ganache, chop the 120 g chocolate. Heat the weighed 90 g cream until steaming strongly with the first small bubbles around the edge, pour it over the chocolate and wait a minute. Stir from the center until smooth. Leave for about 20–30 minutes, until it thickens to a soft, spreadable consistency.

In a small saucepan, heat the 100 g milk with half the sugar for the buttercream, or 30 g, until steaming with small bubbles around the edge. In a bowl, mix the four yolks with the remaining 30 g sugar; do not beat into a foam. Gradually pour in the hot milk, stirring, then return everything to the saucepan. Cook over low heat for about 4–6 minutes, stirring without stopping with a spatula across the bottom and around the sides, until the base thickens noticeably and coats the back of a spoon, and a line drawn through it does not immediately close. Do not bring to a boil. Immediately take off the heat, add the 4 g coffee and stir.

Pour the hot base into a clean bowl standing in cold water and stir for about 10–15 minutes, until cooled to lukewarm and no longer warming the bowl; make sure no water gets inside. The butter should be soft, yielding easily to a spatula, and at a similar temperature to the base, but it must not be liquid. Beat all 180 g butter for about 2–3 minutes, then add the coffee base a spoonful at a time, beating and scraping down the sides. Beat until smooth and fluffy. Do not combine butter with the hot base. Divide the finished buttercream into two equal parts.

Melt the reserved 20 g chocolate in a small dry bowl over hot water, without letting the bottom touch the water. Spread very thinly over one side of the first sponge layer. Refrigerate for about 10 minutes, until the chocolate sets. Then turn the sponge chocolate-side down and place on a flat board or plate large enough for the whole cake. This thin layer stays in the dessert. Do not add any extra oil or butter to it.

Soak the top of the first sponge with about 45 g prepared coffee syrup and spread half the coffee buttercream over it. Cover with the second sponge, press gently and apply another approximately 45 g coffee syrup. Spread all the soft ganache over it, leveling the layer without mixing it with the buttercream below. Add the third sponge, press lightly, soak with the remaining approximately 45 g coffee syrup and cover with the second half of the coffee buttercream. Level the top with a spatula. All three sponges and their fillings should sit evenly above one another; if the buttercream starts softening in a warm kitchen, chill the cake for about 10 minutes before adding the next sponge.

Cover the cake with a tall container or cover that does not touch the buttercream and immediately refrigerate for at least 4 hours, preferably overnight. Do not trim the soft cake. During chilling, the butter and ganache will set and the coffee syrup will spread through the sponge. Prepare the glaze only when the top is cold and clearly firm.

Chop the remaining 70 g chocolate and melt it with all 10 g oil in a dry bowl over hot water. Remove the bowl and stir for a few minutes until the glaze is still fluid but no longer hot. Pour onto the cold coffee buttercream top and quickly spread all of it into a thin layer, without going over it repeatedly. Do not coat the sides and do not add decorations. Refrigerate for about 20–30 minutes, until the top sets.

Using a long sharp knife warmed in warm water and thoroughly wiped dry, trim all sides to make a rectangle about 12 × 28 cm with even exposed layers. Set the trimmed strips aside outside the dessert servings. Cut the cake into twelve rectangles about 4 × 7 cm, warming and wiping the blade between cuts. Before serving, let the portions stand outside the refrigerator for about 10–15 minutes. Keep the remaining Opera covered in the refrigerator and eat within 2 days of preparation.