Hydrate the gelatin powder in the smaller portion of water.
Use the larger portion of water and sugar to make a syrup, then infuse the mint leaves for approx. 20 minutes.
Strain, then add the lime juice, half of the rum, the ginger and the gelatin. Bring to the boil.
Leave to cool then add the remaining rum.
Leave to set overnight in the refrigerator.
Beat in a stand mixer until the syrup has the texture of a mousse. This can take approx. 45-50 minutes.
Pour into a frame.
Store in the freezer.
Turn out and cut into cubes.