Step 1

Gather all the ingredients.

Step 2

Sometimes, life happens and you just don't have 20 minutes to make dashi from scratch. On those occasions, you can use a Dashi Packet or Dashi Powder.

Step 3

Gather all the ingredients. Most Japanese recipes would say to gently clean the kombu with a damp cloth. However, these days, kombu is quite clean, so just make sure it doesn't have any mold spots and it's ready to use. Do not wash or wipe off the white powdery substance, as it has lots of umami. Put the water and kombu in a large bottle or measuring cup and let it steep on the counter for at least 30 minutes (or ideally, 2-3 hours in the summertime and 4-5 hours in the wintertime). You can also cold brew the kombu dashi overnight in the refrigerator.

Step 4

Add the kombu and water to a medium saucepan. If you have cold brew Kombu Dashi (previous step), add the Kombu Dashi and hydrated kombu to the pot.

Step 5

Turn on the heat to medium low and slowly bring it to almost boiling, about 10 minutes. Just before the dashi starts boiling gently, remove the kombu from the pot (discard or repurpose it in other recipes—suggestions follow). If you leave the kombu in the pot, the dashi will become slimy and bitter.

Step 6

Add the katsuobushi and bring it back to a boil again. Once the dashi is boiling, reduce the heat, simmer for just 30 seconds, and turn off the heat.

Step 7

Let the katsuobushi sink to the bottom, for about 10 minutes. Meanwhile, you can prepare the soup ingredients.

Step 8

Strain the dashi through a fine-mesh sieve over a bowl or measuring cup. The Awase Dashi is ready to use.

Step 9

Reserve the spent kombu and katsuobushi in an airtight container and store it in the refrigerator for a week or in the freezer for up to a month. See the instructions below for how to repurpose them.

Step 10

Tips: The ingredients I use here do not require pre-cooking. If you want to add different ingredients to Osumashi, be sure to first cook separately any ingredients that require cooking, then add them to the soup later. These include dense root vegetables or leafy greens that may release color, such as spinach. Once all the ingredients are cooked, simply add them to the clear soup to warm up.

Step 11

Soak the fu (wheat gluten) in water for 10 minutes. Once soft, gently squeeze out the water.

Step 12

Discard the stems of the shiitake mushrooms and thinly slice them about ¼ inch (6 mm) thick.

Step 13

Make a knot in a mitsuba stem and repeat it for the rest of the sprigs. Detach the wooden board of the kamaboko by sliding the knife under the fish cake. Then, cut the kamaboko into thin ⅛-inch (3-mm) slices.

Step 14

Add the rehydrated wheat gluten and mitsuba to the individual bowls.

Step 15

Next, make the clear soup broth: Add the Awase Dashi back to the pot and season with the soy sauce and salt.

Step 16

Add the kamaboko fish cake slices and shiitake mushrooms to the pot and heat until warm. Serve the soup in the individual bowls.

Step 17

Enjoy!

Step 18

Let your soup cool to room temperature and then refrigerate for up to 2-3 days. It's best to add the mitsuba and wheat gluten just before serving.

Step 19

With the spent kombu, you can make Simmered Kombu (Kombu Tsukudani).

Step 20

You can also repurpose the spent kombu and katsuobushi to make Homemade Furikake (Rice Seasoning).