Cook the cha soba noodles according to the instruction on the package. Cook according to the timing on the package or the desired tenderness. Mine said to cook for 6 minutes, check yours. Rinse the noodles well with cold water and set aside
Prepare the men tsuyu sauce by bringing 2 cups of water to a boil. Add in the shiitake mushrooms and lower the heat to let it gently simmer for 5 minutes. Add in the soy sauce, sake, mirin, and sugar and let it cook for another 5 minutes. Remove the shiitake mushrooms from the pan, and slice into smaller pieces and place them back into the pot. Turn off the heat
Serve the noodle warm or cold. Sprinkle with some spring onion and grated ginger and with men tsuyu on the side