Reserve a few blueberries for decoration. Put the remainder of the blueberries in a food processor or blender with the yogurt, icing sugar and lemon rind and juice and process until smooth.
Spoon the mixture into a 600 ml (1 pint) freezerproof container and freeze.
Eat when the frozen yogurt is softly frozen and easily spoonable. Before serving, decorate with the reserved blueberries and a sprinkling of icing sugar. Use within 3 days.