Mix gelatin with 30 ml of cold water. Leave to swell for 5 min. Add 40 ml of warm water and hold in a water bath, stirring to dissolve the gelatin. Cool down a bit.
Peel the mango, cut the pulp from the stone and beat in a blender with cream and sugar until smooth and fluffy.
Pour the gelatin into the mango puree, beat again and pour into 4 glasses or bowls. Refrigerate for 2 hours. The mousse should set. Garnish with mint and serve.