Tiramisù cake

Sponge fingers

In the stand mixer, with the whisk, start whipping the egg whites; when they begin to take shape, add the sugar and keep whipping really well. At this point fold in the yolks and then, by hand, the flour sifted together with the starch. Using a spatula, transfer the mixture to a piping bag without a nozzle. Cut the tip to a width of about one centimetre and pipe three discs of about 24 cm in diameter (starting from the centre, pipe a spiral until you reach that size) onto trays lined with baking paper. Dust with caster sugar and bake each disc for about 15 minutes at 180°C.

Mascarpone cream

Make a syrup with the sugar and the water and bring it to 121°C on the heat, checking the temperature with a thermometer. When the temperature reaches about 115°C, start whisking the yolks, then pour the syrup over them and whisk well (pâte à bombe). When the pâte à bombe is cold, gently fold in the mascarpone and the whipped cream until you have a smooth, firm cream.

Dark chocolate and coffee cremoso

Put the cream with the instant coffee in a small pan and heat it; meanwhile whisk the yolks with the sugar and pour them into the cream. Cook to 83°C, checking the temperature with a thermometer. When the temperature drops back to about 60°C, add the gelatine, soaked and squeezed out beforehand, and the melted dark chocolate. Leave to rest in the fridge.

Chocolate sphere

Melt the chocolate at about 50°C, then lower the temperature to 32°C. Pour it into the polycarbonate half-sphere mould and tip out the excess chocolate by turning the mould upside down and shaking it over a tray. Leave to set in the fridge, then take out the half-spheres.

Assembling the cake

With a 22 cm metal ring, cut out the three sponge finger discs. Line the inside of the ring with acetate and place it on a plate. Lay the first disc of sponge, soak it with unsweetened coffee and pipe over it a layer of mascarpone cream 1 cm high, using a piping bag. Make a layer of cremoso, again with a piping bag. Continue with the second layer of sponge, coffee soak, mascarpone cream and cremoso, finish with the last disc of sponge and decorate the surface with spikes of mascarpone cream and small tufts of cremoso. Put in the freezer for a few hours. Place on a serving plate, remove the ring and the acetate strip and dust with unsweetened cocoa. Decorate the surface with a half-sphere filled with mascarpone cream and another half-sphere placed on top.

Notes

If you have some sponge finger mixture left over, you can make actual sponge fingers to use in other preparations.