Put the sweet potato in a rice cooker with 500 ml of water (not listed). Press Start and wait until the cooking is finished. Check with a skewer to see if it's cooked through. If it is not cooked enough press the Start button again until it's done (you can also microwave or boil the sweet potato if you'd prefer).
Peel the sweet potato and mash. Add salt and maple syrup and mix well.
Make the kanten solution. Combine water and kanten in a sauce pan and bring to a boil, stirring with a balloon whisk. After bringing to a boil, reduce the heat to low and continue to cook and stir for 1 minute.
Take 3 tablespoons of the kanten solution and add to the adzuki bean paste. Mix well.
Transfer the bean paste to a container (I use a 15 x 10 x 4 cm plastic container). Flatten the surface and get rid of bubbles.
Add the rest of the kanten solution to the sweet potato mash. Mix well.
Transfer Step 6 to the container with the bean paste (make sure the anko has settled for at least 2 minutes before to let it settle a little and it will be easier to form). Press down tightly and do not leave bubbles between the adzuki and sweet potato.
Place in the fridge and chill until set. (It will set even at room temperature.)
Story Behind this Recipe
Cookpad user Bubukun's recipe, "Sweet Carrots in the Rice Cooker" gave me the idea of cooking sweet potato like this.
Adjust the amount of maple syrup to taste. When you put the mixture into a container, it is important to remove bubbles. Otherwise it won't be set cleanly. I did several trials and found the sweet potato sweetest after baking in the oven. Unfortunately, it takes time so I cooked in a rice cooker instead. The sweet potato cooks nicely in a rice cooker too.