For the mousse, place the papaya flesh into a blender and blend to a purée. Whip the cream together with the vanilla seeds until stiff peaks form when the whisk is removed. Fold in the puréed papaya and chill.
For the raisin butterscotch sauce, heat the caster sugar in a frying pan. Add the raisins and cook over a gentle heat until the caramel begins to bubble. Stir in the butter and, when melted, stir in the cream. Cook for a few more minutes until the sauce thickens and turns a golden-brown colour.
To serve, spoon the raisin butterscotch sauce into the base of a glass and fill up with the papaya mousse. Garnish with a sprig of fresh mint.