800g/11lb 12oz seasonal mixed berries, such as raspberries, strawberries, gooseberries, blackberries or redcurrants
2 oranges, juice and grated zest
475g/1lb 1oz caster sugar
3 tsp cornflour
Icing sugar, for dusting
2 tsp white wine vinegar
600ml/1 pint 1fl oz double cream
8 free-range egg whites