Bring 1/4 cup water and the superfine sugar to the boil. Once the sugar has dissolved, remove from the heat. Add the gin, tonic, lemon juice and grated Bramley apples. Set aside to cool completely, then pour the mixture into a plastic freezer-proof container and place in the freezer.
Every 30 minutes, remove the container from the freezer and whisk the mixture. Repeat this until it is frozen (this will take 3 to 4 hours).
To make an apple caramel, heat the apple juice until it is reduced in volume to a thick caramel (this will take approximately 45 minutes). Remove from the heat, and whisk in the butter. Leave to cool.
To serve, remove the granita from the freezer and break it up with a fork to create a slushy texture. Sprinkle the diced Braeburn apples on top, and serve with the apple caramel.