How to Make It
Soak the rice in a large bowl of water overnight. In a large pot, combine the kombu with all the dried mushrooms and 3 quarts of water; cover and let stand overnight.
Bring the pot of kombu and mushrooms to a simmer over moderately high heat. Immediately remove the kombu and discard. Simmer the stock until reduced to 4 cups, about 1 hour. Strain the stock and discard the mushrooms (or reserve them for another use). Season lightly with salt.
Meanwhile, drain the rice and shake out the water. Let the rice air dry for 30 minutes, shaking it in the strainer occasionally.
Preheat the oven to 450°. On a rimmed baking sheet, toss all the fresh mushrooms with the 3 tablespoons of melted butter and the soy sauce. Roast for about 20 minutes, stirring once or twice, until the mushrooms are tender and browned in spots. Let cool slightly, then coarsely chop the mushrooms.
Line a large bamboo steamer with cheesecloth. Spread the rice over the cheesecloth in a 1-inch-thick layer. In a small bowl, combine 1/4 cup of the sake with 1/2 teaspoon of salt. Sprinkle the mixture over the rice. Set the steamer over a pot of boiling water and steam the rice over high heat until the grains are al dente and translucent, 8 minutes. Let cool slightly, then break up any clumps.
In a large, deep skillet, heat the remaining 3 tablespoons of butter. Add the onion and cook over moderately high heat, stirring occasionally, until softened, about 5 minutes. Add the chopped mushrooms and cook for 2 minutes, until sizzling. Stir in the steamed rice. Add the remaining 1/4 cup of sake, season with salt and pepper and cook until the sake is absorbed, about 1 minute. Add 1/2 cup of the mushroom stock and cook over moderate heat, stirring, until absorbed. Add another 1/2 cup of the stock and cook, stirring, until the rice is tender but not mushy, about 10 minutes; you will have stock left over for another use. Stir in the chives and serve right away.
The recipe can be prepared through Step 5; refrigerate the cooked rice and strained mushroom stock separately for up to 2 days.
Pearl rice is glutinous (sticky) rice. Kombu is edible kelp. They are both available on amazon.com.