Cut the sweet potato into 1.5cm cubes. Soak in water to get rid of the bitterness, then drain.
Put the sweet potatoes in a pot with just enough water to cover them. Add the brown sugar and heat. Heat over high heat until it comes to a boil, then reduce to medium. Skim off any scum that forms.
Once the sweet potatoes are about 80% cooked, gradually add the katakuriko slurry, a little at a time, to achieve a firm thickness. Be careful not to crush the potatoes.
Transfer to a serving plate. Eat with a spoon. They're really hot right out of the pot, so be careful not to burn yourself!
This is what they should look like after they cool. They are no longer glossy, but sweeter.
And this is what they should look like after refrigerating for a day The glossiness is gone, but they are moister and sweeter and easier to enjoy.
Story Behind this Recipe
This is a simple snack that my mom made for me when I was young.
Beyond giving these a creamy texture, the purpose of katakuriko, is to give the sauce a firmer texture (similar to slime). Be careful not to over-boil the potatoes in Step 2! Adjust the amount of sugar and water to your liking. These are easier to make than oni-manju.