Place 175g of sponge fingers in a serving dish (I use a 5cm-deep dish measuring 24cm x 16cm), breaking them up and squeezing them into the gaps where necessary so the base of the dish is covered. Stir 200ml of orange juice and 60ml of fino sherry together, then spoon it evenly over the sponge fingers. Cover the dish and set aside for 30 minutes.
Using a fork, mash 250g of raspberries to a thick purée, then spoon over the sponge fingers.
Separate 3 eggs, and put the yolks in the bowl of an electric mixer and the whites in a large mixing bowl. Add 4 tbsp of sugar to the yolks and beat until thick and creamy with the whisk attachment, then blend in 500g of mascarpone and a few drops of vanilla extract. Stop the mixer.
Beat the egg whites until thick and foamy, almost stiff. Now fold them, using a large metal spoon, into the mascarpone mixture until incorporated.
Spread the mascarpone mixture on top of the crushed raspberries and sponge fingers, cover the dish again and leave in the fridge for at least a couple of hours, preferably overnight. When you’re ready to serve, whip 250ml of double cream and decorate with a further 150-200g of raspberries. Serves 6-8
Take care when folding the beaten egg whites into the mascarpone mixture. You want to make certain there is no egg white visible, but also be careful not to overmix.
You can eat this tiramisu within an hour or two of making it, but it is far better if you can give it an overnight stay in the fridge before adding its final top layer of cream and extra fruit. The longer the sponge has to soften with the fruit and boozy juice, and the layers have to combine, the better.