Photograph: Martin Poole
Whisk the egg yolks and sugar together until thick and pale – this should take about 10 minutes. Add the mascarpone and whisk again until combined.
In a separate bowl, whisk the egg whites to the soft peak stage. Mix a heaped tablespoon of the egg whites into the mascarpone mixture, then gently fold in the rest.
Stir the brandy into the coffee in a shallow dish. Soak one-third of the biscuits in the coffee mixture for about 10 seconds, then put a layer into each of eight tumblers or small dishes, halving the sponge fingers if you need to. Top with a layer of the mascarpone mixture, then repeat the process twice. Chill well. It's fine to make the tiramisu the day before you want to serve it.
Melt the chocolate and spread it out on a baking tray. Chill, then run a kitchen knife across the hard chocolate to make curls. Top each serving of tiramisu with chocolate curls and dust with cocoa.
Get ahead: you can make the tiramisu the day before. Top with chocolate curls and cocoa just before serving. You can also freeze the tiramisu in a freezer-proof dish or dishes. Defrost at room temperature for 4-5 hours, then chill if not serving straightaway.
Kitchen secret: the dusting of cocoa is traditional; the chocolate curls are not essential but they do look pretty. If you want both and are short of time, grate the chocolate over the top instead.
Note: this recipe contains raw eggs.