Place boiling water in a small jug or similar. Carefully sprinkle in gelatine powder while whisking constantly. Dissolve gelatine as much as possible. If there is still a bits of gelatine floating around or undissolved, microwave for 30 seconds and whisk again. Add cold water and whisk to combine.

Place moulds on a baking tray so they lie flat. Using pipette, carefully fill moulds. Carefully pop any large air bubbles floating on the surface of the bottles with the end of the pipette. If any liquid has spilt out around the bottles, use a piece of paper towel and just gently touch the towel to them to soak the liquid up.

Place tray with moulds lying flat in the fridge. Refrigerate for 1-2 hours or until set. Remove from fridge and gently pop out the coke bottles from the moulds.