To make the sorbet, dissolve the sugar in the water over a low heat. Bring to the boil and boil gently for 10 minutes. Add 1 tablespoon lemon juice. Put the rinds in a basin, pour over the boiling syrup and leave till cold. Add the juices and freeze. When half frozen, fold in the whisked egg whites. Continue freezing.
For the ice cream, stand the tin of condensed milk, unopened, in a pa