Miso Soup With Satsumaimo (Japanese Sweet Potato)

A traditional miso soup built on a 10 minute kombu and katsuobushi dashi, with thick rounds of satsumaimo and thin sliced onion. Brothy and chunky, never blended.

Course Soup

Cuisine Japanese

Keyword miso soup with satsumaimo

Prep Time 10

Cook Time 20

Total Time 30

Servings bowls

Ingredients

For the Dashi

4 cups cold water
1 piece kombu about 4 inches square
1 packed cup katsuobushi dried bonito flakes, about ½ ounce

For the Soup

2 small satsumaimo Japanese sweet potatoes, about 11 ounces total, scrubbed and sliced into ½ inch rounds
1 cup yellow onion thinly sliced
4 tablespoons white or yellow miso to taste
2 scallions thinly sliced
1 pinch shichimi togarashi optional, at the table

Instructions

Make the Dashi

Put the cold water and the kombu in a saucepan and bring it slowly to just below a simmer over medium-low heat, about 8 minutes. Pull the kombu out as soon as small bubbles climb the sides. Do not let it boil.
Turn off the heat, add the katsuobushi, and let it stand 2 minutes while the flakes sink. Strain through a fine sieve without pressing the flakes, and return the dashi to the pot.

Simmer and Season

Slice the scrubbed satsumaimo into ½ inch rounds with the skin on. Rinse the rounds briefly under cold water to remove surface starch, then drain.
Add the potato rounds and the sliced onion to the dashi. Bring to a gentle simmer over medium heat and cook 10 to 12 minutes, until a skewer slides through a round with no resistance. Stir as little as possible.
Turn the heat off. Ladle a little hot broth into a small bowl, whisk the miso into it until completely smooth, then stir that back into the pot. Never let the soup boil after the miso goes in.
Divide between four bowls, scatter the sliced scallion over the top, and serve immediately with shichimi togarashi at the table.

Notes

Never boil the kombu: Pull it at the first bubbles or the dashi turns slimy and bitter.
Never boil the miso: Dissolve it in a ladle of broth and stir it in with the heat off. Boiling flattens the aroma and turns the soup grainy.
Cut ½ inch rounds: Thinner rounds fall apart, thicker rounds go mushy outside before the center cooks.
Skin on: It holds the rounds together and the purple against the pale flesh is the look of the dish.
Shortcut dashi: 1 teaspoon of instant dashi granules per 4 cups of water, or a dashi packet steeped 5 minutes.
Storage: 3 days in the fridge. Reheat to steaming only, never to a boil.