In a bowl add the granulated sweetener to the frozen raspberries, mix well and place covered in the fridge overnight. This will help the raspberries break down to make a sauce.
Place frozen mango and frozen banana into a food processor and blitz until smooth.
Transfer to a lidded plastic tub and place back into the freezer until ready to serve.
Remove the ice cream from the freezer 10 minutes before serving to soften a little, then serve topped with the sweetened raspberries.