• Gather all the ingredients.
  
• Cut the green onion into thin rounds.
  

To Make the Dashi (Can Be Made in Advance)

• Add the water and kombu to a medium saucepan. If you have time, soak the kombu in water for 30 minutes. NEVER wash kombu and do not remove the white substance—that’s umami! These days, it's pretty clean so just make sure there are no dirt particles.
  
• SLOWLY bring it to a boil on medium-low heat so you can extract as much umami from the kombu as possible (about 10 minutes). Right before the stock boils, remove the kombu and set it aside for another use. (If you leave the kombu, it gets slimy and yields a bitter taste.) Now, what you have is Kombu Dashi. If you’re vegetarian/vegan, use this kombu dashi for your miso soup.
  
• If you're not vegetarian/vegan, add the katsuobushi to the kombu dashi and let it simmer for 1 minute.
  
• Turn off the heat and strain through a fine-mesh sieve. Reserve the spent katsuobushi for another use.
  
• Now you have roughly 4 cups of Awase Dashi. You can store the dashi in the refrigerator for up to 3-5 days and in the freezer for up to 2 weeks. Repurpose the used kombu and katsuobushi to make Simmered Kombu or Homemade Furikake Rice Seasoning.
  

To Make the Miso Soup

• Add the dashi to the saucepan. If you are using premade dashi, bring it to simmer over medium heat and turn off the heat.
  
• Add the miso (typically, use 1 Tbsp miso for every 1 cup (240 ml) of dashi). Put the miso in a ladle, slowly add the dashi into the ladle, and stir with chopsticks to dissolve the miso completely. Here, I'm using a miso muddler. If you accidentally add too much miso, dilute the miso soup with dashi (or water). 
  
• Here, I'm using a fine-mesh miso strainer, which helps you dissolve the miso faster. After dissolving the miso in the strainer, you may see rice koji (especially when it's koji miso). It's up to you if you want to include it in the miso soup or discard it (personal preference).
  
• Cut the tofu into ½-inch (1.3 cm) cubes and add to the miso soup. Tip: Add the tofu after the miso is completely dissolved; otherwise, you might break the tofu when stirring in the miso. Note: It is very common to cut tofu on your palm in Japan. However, it's not required and I recommend using a cutting board if you have never done this.
  
• Add the dried wakame seaweed. Reheat the miso soup until it is just hot. NEVER BOIL miso soup because it loses nutrients, flavor, and aroma. Add the chopped green onions right before serving to keep their fresh fragrance and color. Tip: If you worry about salt intake, I recommend rehydrating the dried wakame in a separate bowl of water to get rid of the saltiness, instead of rehydrating it in the soup itself.
  

To Serve

• Serve immediately. Place on the right side of the table setting (read about this on Ichiju Sansai (One Soup Three Dishes)).
  

To Store

• In general, it's best to consume all the miso soup right away because it will lose its aroma and taste as time passes. Let your miso soup cool to room temperature (up to 4 hours; any longer and it will spoil) and then refrigerate. Keep for up to 2 days in the refrigerator. If you want to make a big batch to store for later, it's best to refrigerate the soup without adding the miso. When ready to use, add the miso only for the portion you need. You can freeze miso soup for up to 2 weeks. However, you have to remove the tofu before freezing as the texture will change.

To Reheat the Miso Soup

• Heat the miso soup in a pot over medium heat, but do not boil. Miso loses its nutrients, flavor, and aroma at high temperatures.