G&T granita

What’s better in SUmmer than granita? This recipe from suzanne farrell takes it to new heights!
220g castor sugar
120ml water
Juice of one lemon including fleshy bits
Juice of one lime including fleshy bits
(made up to 500ml with cold water)
200ml gin
80 – 100 ml sin-ko-nah tonic syrup (or to taste)
1/2 granny smith apple*, peeled, cored and very finely diced (about 5mm square or smaller if you can or grated – including the juice as well
*The apple gives the granita a bit of balance with some sourness and some body. You could use the whole apple if you like the result.  
Mix castor sugar and 120ml water in a pan over a medium heat and stir until the sugar is dissolved.  Bring to a steady boil for 5 mins. Take off the heat and cool for 10 mins.
Stir in cold water, citrus juices and pulp, add the gin and tonic syrup. Keep tasting as you add things until you’re pleased with the flavour – remembering that it will taste less sweet and less alcoholic when frozen.
Add the apple pieces (and juice if you grated the apple) and stir.
Pour into a freezer safe container – a large and flat tray is most efficient but anything that fits in your freezer will do. Freeze for 30 mins – then take it out – pour it into a saucepan  and whisk for a few seconds. Then  return to freezer for another 30 mins. Continue to do this until the granita is pretty firm and frozen, but not solid like ice. This will take 3 – 4 hours.
To serve, use a fork to break up the granita into icy cold lumps. You can store the left over granita in the freezer for a month or so. Break it up with a fork before you put it in the freezer and also before you serve it.
I serve this as a drink in a chilled martini glass, with an extra shot of gin, or limoncello, and a thyme sprig as garnish. Or you could make it the base of a dessert with lemon gelato scoops and shortbread biscuits.