1) Make dashi, if not using instant.How to Make Kombu (Kelp) Dashi (a Japanese vegetable broth made with kelp): Soak 1/2 ounce (15 grams) dried kombu (don't rinse first, it'll get rid of the flavor!) in 4 cups water for 2 hours. Put kombu and water in a cooking pot and bring to a boil over medium heat. When water boils, remove kombu with a strainer. The remaining liquid is your kombu Dashi. The removed kombu can be used to cook in other recipes.
How to make Shiitake Dashi (a Japanese soup broth made with dried shiitake mushrooms): Soak 1/2 cup (4 ounces) shiitake mushrooms in 4 cups water for 30 minutes. Put shiitake and water in a cooking pot and bring to a boil over medium heat. When water boils, turn off heat and let mixture stand for 30 minutes. Remove shiitake with strainer. The remaining liquid is your shiitake dashi. The removed shiitake mushroom can be used to cook in other recipes.
2) Heat your pot with the dashi stock over low heat. Add tofu and wakame seaweed. Allow seaweed to simmer in soup until tender (Wakame seaweed looks like slippery spinach. It is thin, deep green, and most often sold either fresh or dehydrated.) You can add small slices of shiitake if you want.
3) Once seaweed is tender, turn off heat. Stir miso into broth, little by little. Your broth should be cloudy looking. (By turning off the heat you wont have to worry about burning or over cooking the miso.)
4) Put your soup into a bowl and add green onions while its still hot! Wait half a minute before consuming to allow the juice from the onion to flavor the broth. (This method allows it to flavor the broth but at the same time keeps the onion fresh tasting instead of soggy.)
Happy Eating. Don't forget to say ''itadakimasu'' before eating and ''Gochisou-sama'' once finished. :)
Source of recipe: i found this recipe long time ago but cant remember where from but i have modified it and made simpler directions.