Use an electric whisk to beat the egg yolks with half the sugar until the mixture is pale and moussey – this will take 3-4 mins. Beat the mascarpone in a large mixing bowl to loosen, then beat in the double cream until just combined. Scrape in the mousse mixture and beat everything together until smooth and light.
Clean the beaters, then whisk the egg whites in another bowl until stiff peaks hold on the end of the beaters. Tip in the remaining sugar and beat until glossy and stiff again. Use a big metal spoon to stir a third of this into the cream mixture, then gently fold in the rest.
Get your serving dish or bowl ready, then put the Marsala in a shallow plate and dip in a few sponge fingers at a time so they are just soaked but not soggy. Layer half of the fingers evenly in your dish, then scatter over half the fruit. Top with half the cream mixture, then crumble over half the crunchy amaretti biscuits. Repeat the layers, but finish with the cream and save the other half of the biscuits. Cover and chill for a few hrs, or overnight.
To serve, crumble over the remaining biscuits, then spoon into bowls.