Place 100g of caster sugar and 450ml of the Coca-Cola in a medium saucepan. Bring to the boil over a medium heat. Allow the mixture to cool to one side.
Heat 50ml of the Coca-Cola in the microwave on a high power for 10 seconds. Remove and stir in the powdered gelatin. Mix together with the boiled Coca-Cola mixture and distribute evenly between 6 serving glasses. Place in the fridge and allow to set.
Meanwhile, prepare the lemon sorbet by combining 250g of the caster sugar with 325ml of water in a medium saucepan. Heat gently over a medium-low heat until the sugar has dissolved and then simmer for 2 minutes. Stir in the lemon juice and reserve to one side. Churn the liquid in an ice cream machine until it reaches a sorbet consistency. Freeze until needed.
Prepare the Coca-cola sherbet ice by pouring the remaining Coca-cola into a shallow plastic tub. Freeze for 1 hour and then use a fork to break up the semi-frozen Coca-cola. Refreeze the semi-frozen Coca-cola for another hour. After one hour, remove the lemon sorbet and place a scoop on top of the Coca-cola jelly.
Top with a scoop of the frozen Coca-cola. Arrange a few strips of lemon zest on top of the Coca-cola sherbet. Serve with straws.