Begin the dashi, if using, the previous day, by soaking the seaweed in the 4 cups of water overnight.
Next morning, heat the water with the dashi in it. When the water is about to come to a boil, remove the pieces of dashi with a pair of tongs. Set the stock aside.
In a medium saucepan, heat 1 tablespoon of the dashi stock with the ginger, turmeric and carrots. Saute, stirring frequently, for a couple of minutes or until the stock has dried up.
Measure out a cup of the dashi stock and mix the miso paste in it until everything's well-dissolved. Set aside.
Pour the remaining dashi into the saucepan with the ginger, turmeric and carrots, stir, bring it to a boil, and let it cook for about eight minutes.
Add the tofu cubes and bring back to a boil.
Add the scallions or coriander leaves and turn off the heat.
Stir in the miso paste.
*Miso tends to collect at the bottom if the soup sits too long, so stir it up once before serving.