Heat oil in a pan. Add the new potatoes and stir-fry over medium heat (about 5 minutes). The potato skin becomes wrinkly when it's thoroughly cooked, so fry until you see that.
Add water and boil until you can poke through the potatoes with a skewer (about 15 minutes).
When there's not enough water, gradually add while it's simmering.
There should constantly be enough water so the potatoes are halfway covered.
When the potatoes are tender, dissolve the sugar and miso. Simmer and reduce over high heat. It's done when the broth has thickened .
About the miso: I use country-style miso that's slightly saltier than normal miso. It's similar to koji miso.
If you're using either sweet or white miso, adjust the amount of sugar to about 1 to 1 1/2 tablespoons.
This is how it looks when you use ready-made blended miso (Kanto region style).
Each miso has its own flavor, so taste and experiment.
Warning: When there's too much oily water in Step 4, the miso will splatter. Use just enough water to dissolve the miso, and discard the rest.
Story Behind this Recipe
My family has been making this dish for generations. I make it every week when new potatoes are in season. My father and husband don't even like potatoes, but they like this dish! It goes well with rice as well as drinks.
I use homemade country-style miso that has a very strong salty flavor. If using sweet miso, adjust the amount of sugar. The key to this recipe is to stir fry the potatoes very, very well.