For the dashi keep water and dried mushrooms to soak. If you have kombu seaweed, add that too. Keep to soak for at least 2 hours (we soaked 6 hours). If you are in a hurry, soak with warm water for 30 minutes.
When done soaking, discard mushrooms (and kombu if you added that earlier). Keep dashi on the stovetop and heat up.
The dashi will form foam. Skim foam with a fine mesh.
Add soy sauce, sugar and salt to the dashi and combine while it's still cooking.
Reduce heat completely or take from heat when it's bubbling and add in the miso paste. Mix paste into your hot soup.
Take miso soup from the heat, garnish with sliced green onion stalks and serve hot.
You can add kombu, it's optional. The recipe video doesn't include kombu. kombu with shiitake is a great combination and gives a lot of flavor to the soup. To use the kombu, just take it once through running water and add to the water with the mushrooms.
Use red or white miso paste or mixed. If you are using a high quality flavorful miso, you won't need to add the soy sauce, sugar and salt. Never boil the miso paste or else it will change the flavor of your soup. Add at the end so that the miso paste won't get accidently boiled.
You can choose to add more ingredients during the cooking process (but before the miso past is added, miso paste always at the end), such as tofu, vegetables, meats, seafood. See post for ideas.
The servings are small japanese sized bowls. Two of these japanese servings equal 1 large serving in the West.