BLOOM THE GELATINE: To make the jelly, line a 20x30 cm dish with clingfilm and set aside. Soak the gelatine sheets in a large bowl of cold water.

MAKE THE JELLY: Heat the tonic water in a medium saucepan until warm, then squeeze out the gelatine sheets and add to the tonic, one at a time, stirring until dissolved. Pour the gin into the saucepan and mix well, then remove from the heat and set aside to cool to room temperature.

CHILL AND SET: When the jelly mixture is cool, pour into the prepared dish and chill in the fridge until set. This can be made in the morning ready for the evening, but I suggest letting the jelly set at least 24 hours.

MIX THE GRANITA: To make the granita, first put a glass baking dish (Pyrex etc) in the freezer to chill. Place the sugar, lemon zest and water in a medium saucepan. Heat gently, stirring until the sugar is dissolved. Remove from the heat, stir in the lemon juice. If you like the granita extra tart, add up to 1 tsp citric acid, but remember it will be less sweet when it freezes.

STIR THE GRANITA: Pour the mixture into the chilled dish and set a timer for 1.5 hours. When the timer is up, take the dish out of the freezer and use a fork to gently bring the ice crystals that have formed around the outside into the middle of the dish.

REPEAT: Repeat at half-hour intervals until the mixture is entirely frozen - this will take up to 4 hours, but the active work only takes seconds. You will end up with a big bowl of delicious, lemony, icy crystals. When the granita is fully frozen, cover the dish and keep in the freezer until needed.

SERVE: To serve, lift the jelly out of the dish and use a thin, sharp knife to cut it into cubes. Divide the granita between 4-6 chilled glasses, top with the jelly ‘ice cubes’ and garnish with a thin slice of lemon and a sprig of mint. Spoon an extra teaspoon of granita over the top of each, then serve immediately.