For the finger biscuit layers, preheat the oven to 200˚C (or 180˚C for fan-assisted ovens). Grease and line 3 cake tins (22cm) – or bake them one at a time if only 1 tin is available. Whip the 3 egg whites until stiff peaks form and gradually add the 75g castor sugar to form a meringue. Whip in the 4 egg yolks, then fold in the cake flour and cornflour, taking care not to knock out the air. Add to a piping bag fitted with a 2cm plain nozzle and pipe concentric circles into the tins. Dust with a layer of icing sugar and bake, 8 – 10 minutes, until puffed and golden. Allow to cool before unmoulding from the tins.

Make the espresso syrup by dissolving the 30ml (2 tbsp) castor sugar in the hot coffee. Allow to cool.

For the mascarpone mousse, beat the 3 large (whole) eggs with an electric stand mixer until pale and thick, about 10 minutes. The mixture should leave a trail. Soften the 3 gelatine sheets in water. Heat the 150g sugar, 50ml water and the salt in a small pot, without stirring at all, until it reaches 121˚C on a sugar thermometer. Remove from heat and add the gelatine to the hot caramel, without stirring, then add it gradually into the fluffy eggs, while beating. Whip until the mixture is cool to the touch and thick, about 10 minutes. In the meantime, gradually add the fresh cream to the mascarpone, whisking until thick and smooth. Fold this into the cooled egg mixture.

To assemble, place a cooled finger biscuit layer in the bottom of a 22cm lined springform cake tin. Brush with the espresso syrup until soaked. Pour over half of the mascarpone mousse. Repeat with the finger biscuit layer, syrup and more mousse, finishing it off with the final biscuit layer and a thin layer of mousse. Freeze the cake until firm, about 4 hours.

For the mirror glaze, in a saucepan, combine the 125ml (½ cup) water, 265g sugar, fresh cream and cocoa powder. Simmer, without stirring, about 7 minutes, until the mixture thickens and becomes slightly syrupy. Soften the 5 gelatine sheets in water and add to the hot glaze off the heat. Set over an ice bath and whisk until the glaze thickens to the consistency of double-thick cream and reaches about 26˚C on a sugar thermometer, about 1 minute.

Unmould the frozen mousse cake, by using a hair dryer on a low setting of “hot” to gently warm the pan and unmould easily. Set the cake on a small cake tin on top of a baking tray. Pour the glaze over, all at once, so it runs down the sides. Refrigerate until ready to serve.

To serve, decorate the cake with hazelnut chocolate truffles, chocolate macarons and gold dust.