Place the dried mushrooms in a bowl and cover with 1-2 cups (480 ml) of boiling water.
Let them soak for about 30 minutes (less for porcini) until soft.
Do not discard the soaking liquid.
Heat 2 tablespoons (30 ml / 1 fl oz) of the sesame oil in a large pot or Dutch oven over medium-high heat.
Add the fresh mushrooms and cook, stirring occasionally, until they release their liquid and begin to brown, about 10 minutes.
Drain the rehydrated mushrooms, reserving the liquid.
Slice them and add to the pot.
Cook until they also brown nicely, about 5-10 minutes more.
Add the minced garlic and half of the chopped scallions, cooking for one minute until fragrant.
Carefully strain the reserved mushroom-soaking liquid through a fine-mesh sieve into the pot to remove any grit.
Add enough stock or water to make a total of 6 cups (1440 ml) of liquid.
Bring the soup to a simmer. If using, gently stir in the silken tofu and cook for one more minute to heat through.
Remove from heat and stir in the soy sauce.
Season with salt and plenty of black pepper to your liking.
Serve hot, garnishing each bowl with a drizzle of the remaining sesame oil and the rest of the fresh scallions.
Don't discard the mushroom soaking liquid! It's packed with umami flavor. Just be sure to strain it through a fine-mesh sieve or cheesecloth to remove any grit.
