Step 1

Make the dashi (See step-by-step instructions: How To Make Dashi). Combine the water and kombu in a 1-quart saucepan over medium heat. Remove the kombu just as the water starts to come to a boil. Add the bonito flakes, if using, and let the water come to a rapid simmer. Simmer for about 1 minute, then remove the pan from heat and let the bonito steep for an additional 5 minutes. Strain the bonito from the dashi. Add additional water if necessary to make 2 cups. Alternatively, substitute 2 cups water, chicken broth, or vegetable broth.

Step 2

Prepare the tofu and scallions. Cut the tofu into very small cubes, 1/4-inch to 1/2-inch on each side. Slice the scallions very thinly.

Step 3

Bring the broth to a rapid simmer. Pour the dashi or broth back into the saucepan and bring to a rapid simmer over medium-high heat.

Step 4

Mix the miso with 1/2 cup hot broth. Place the miso in a small ramekin or measuring cup. Scoop out about 1/2 cup of the broth and pour it over the miso. Whisk with a fork or whisk until the miso is entirely dissolved in the water and no lumps remain.

Step 5

Pour the miso into the broth. Pour the dissolved miso into the simmering broth.

Step 6

Add the tofu. Reduce the heat to medium-low and add the tofu to the miso. Simmer just enough to warm the tofu, 1 to 2 minutes. Do not boil the miso once the tofu has been added.

Step 7

Add the scallions. Just before serving, scatter the scallions over the top of the soup.

Step 8

Serve in individual bowls. Pour the miso into individual bowls and serve. Miso is best when served fresh. It will settle a bit as it sits in the broth; whisk briefly with chopsticks or a spoon to mix the soup again.