To make the vodka & lemon granita: Place water, sugar in a small saucepan over a medium heat & stir until the sugar has dissolved. Set aside to cool completely. Stir in the lemon rind, lemon juice & vodka. Place in a shallow metal container. Freeze for 4-5 hours or until completely set. Rake with a fork.
To make vodka & grapefruit granita: Use the same method as above but replace lemon juice & rind with pink grapefruit juice.
Peel and devein prawns, leaving tails intact and serve with granita. Serves 4