With this lightly flavored Yatsugashira yam stew for your New Year's osechi, it's all you need to keep you happy. If you can find Yatsugashira yams regularly, then this is a dish that you will want to make all year round.
Chop the Yatsugashira yam into small pieces, and peel off the skin. It will take a lot of time to peel (although this might just be because I am not used to it). Instead of a peeler, I recommend using a knife that you are more accustomed to peeling with.
Place the pieces of yam into a pot, add enough vinegar water to cover the yams, and bring to a boil over high heat. Gently boiling for a short while, then drain the yams in a sieve.
Return the yams to the pot, fill it with water up to half the height of the yams, cover with a lid, and bring to a boil over high heat.
Once it comes to a boil, reduce the heat, add the sugar and salt, and simmer with the lid on.
After a few minutes, add the soy sauce, and leave covered with the lid until the water content boils down, and it is done.
Story Behind this Recipe
My mother-in-law was preparing this as an osechi dish, and they were really tasty, so I had her teach me the recipe. She taught me to boil them in vinegar diluted in water, then stew them in sugar, salt, and soy sauce. I eyeballed the ingredient amounts, and tried making it myself. It tastes just about as good as she makes it, so I think these amounts will do.
Chopped into large chunks of yam makes it easier to enjoy the distinctively pasty texture of the yams. Use only a small amount of soy sauce, otherwise they will look brown and unappetizing. You can also use Sulawesi potatoes, since there is not much difference in the texture.