Dashi (Japanese Sea Stock)
In a large pot over high heat, add the water, kombu, and other mix-ins (if using)
Bring to the cusp of boiling, without letting it actually boil
Take the pot off the heat, remove the kombu, and sprinkle the bonito flakes over the liquid. Let stand 3-5 minutes, stirring if necessary so the bonito flakes will sink
Strain the stock through a cheesecloth-lined sieve and into a bowl
Stir together miso and ½ cup dashi in a bowl until smooth.
Heat the remaining dashi in a saucepan over low to medium heat until warm, then gently stir in the mix-ins, along with the reconstituted wakame.
Simmer 1 minute and remove from heat.
Immediately stir in miso mixture and scallion greens