1 Line a loaf tin with cling film.
2 Beat the egg yolks with the sugar and vanilla sugar in a bowl over hot water until thick and creamy. Remove from the heat and beat until cold (ideally over a bowl of cold water). Gradually fold in the mascarpone.
3 Whisk the egg whites with the lemon juice until stiff. Likewise beat the cream until stiff and carefully fold the whipped cream into the mascarpone mixture.
4 Fold the cherry purée (reserving 3 tbsp) into 1/3 of the mascarpone mixture. Fold the peach purée (reserving 3 tbsp) into the remaining mascarpone mixture, then fold in the peach pieces and the egg whites.
5 Spread the 3 tbsp of reserved cherry purée over the base of the tin. Tip the cherry mascarpone mixture over the top, pushing it into the edges and making a depression in the centre along the length of the tin. Next spoon the peach mascarpone mixture into the tin and smooth flat. Drizzle the reserved peach purée over the top in streaks.
6 Cover and chill in the freezer for at least 4 hours. To serve, remove from the tin, take off the cling film and cut into slices. Serve stacked with ice cream wafers if desired.