Thinly pare the orange and lemon zest and set
aside for decoration. Cut the fruits in half and
squeeze the juices into a jug. Set aside.
Heat the
sugar and water in a heavy-based saucepan, stirring,
until the sugar dissolves. Bring to the boil, then
boil without stirring until a syrup forms.
Remove
the syrup from the heat, add some of the orange and
lemon zest and shake the pan. Cover and leave to
cool.
Strain the sugar syrup into a shallow freezer
container and add the fruit juice.
Stir well to
mix, then freeze, uncovered, for about 4 hours,
until slushy.
Remove the half-frozen mixture from
the freezer and mix with a fork, then return to the
freezer and freeze again for at least 4 hours.
To serve, turn into a
bowl and leave to soften for about 10 minutes, then
break up again and pile into long-stemmed glasses. Decorate with strips of
orange and lemon zest.