Place pot of water on the stove on a high heat, add sweet potatoes, cover and bring to a boil.
After about 10 minutes, when the sweet potatoes have softened, remove the lid and puncture the sweet potatoes with a sharp paring knife to hasten the cooking process. When done, remove the pot from the heat and pour off the hot water. Cool the sweet potatoes by allowing them to sit in a colander. Alternatively, cool them by placing them under cold, running water.
Cut off the sweet potato's tip and scrape off the skin, using your knife.
With a blender or hand mixer, blend the potatoes and slowly add apple juice to desired texture.
Dissolve agar flakes in 1 glass of apple juice. Mix all together and bring the preparation to a boil for 10 minutes.
Place in individual bowls.