1.Heat kyoko's All-purpose Dashi Soy Sauce Concentrate and water in a medium size saucepan if using, or make the soup by combining the stock, soy sauce, mirin and sake in a large saucepan. Simmer on medium heat for 15 minutes. Turn the heat to low and keep warm.
2.With a wet paper tower, wipe off the mushrooms. Cut the mushrooms with larger surfaces, into ¼ inch slices. Break the shimeji,enoki, and Himeji bunches into small bundles.
3.Heat the butter in a large in a large skillet over medium heat until it is melted. Add the mushrooms and sprinkle on the salt. Stir-fry for 3 minutes, until the mushrooms are just wilted. Turn off the heat
4.Cook the soba noodles according to the instructions on the package. Set a colander in the sink and drain the noodles. Set a large bowl in the sink and add the noodles. Rinse the noodles under warm running water and divide among 4 bowls
5.Turn the heat to high under the mushrooms. Add the soy sauce, toss and cook for one minute. With a pair of chopsticks or tongs, divide the mushrooms onto the top of the noodles.
6.Ladle the soup stock around the soba noodles and garnish with green onions. Serve with Japanese red pepper powder