Reserve 12 small mango slices. Purée the remaining mango slices with the lime juice and ginger in a food processor.
Sprinkle the gelatine over 1/2 cup (125ml) of the water in a small bowl. Let stand for 5 minutes or until softened. Meanwhile, combine the sugar and remaining water in a small saucepan and bring to the boil. Stir the gelatine into the hot sugar mixture and cook, stirring, for 1 minute or until the gelatine is dissolved.
Add the gelatine mixture to the mango purée and process until well combined. Add the sour cream and process briefly just to blend.
Spoon into dessert bowls or glasses, top with the reserved mango slices, cover and refrigerate for 2 hours or until chilled and set.