Cook the sweet potatoes until soft either by roasting in a 400 degree oven for 45 minutes or in the microwave for about 7 or 8 minutes. Let cool. Scoop out the flesh and put in a blender with the cold coconut milk, agave, vanilla, and salt. Blend until smooth. Pour the mixture into an ice cream maker and process according to the manufacturer’s directions. Put ice cream in a covered container in the freezer until firm, at least ½ hour.
Cinnamon Marshmallow Fluff
Combine the water and gelatin in a small bowl and microwave for 30 seconds. Put in mixer with the agave. Turn mixer on low to combine, then increase speed to high and beat for 15 minutes.
Fluff can be stored in a covered glass jar in the refrigerator for up to a week.
Serve ice cream topped with marshmallow fluff and chopped walnuts.