In a pot, heat sesame oil, garlic, and ginger and cook until the garlic releases its own aroma. Add pork and cook. Add shimeji mushroom and cook. Pour dashi stock, soy sauce, mirin, and sake. Just it comes to a boil, lower the heat and simmer. Add white parts of green onion and cook for a minute. Reserve green parts for garnish later.
Bring a large pot to boil for the noodle. Cook the soba noodle according to the instruction of the package. Drain the pot and rinse the noodle with ice water. Once the noodle is chilled, strain it completely.
Divide the noodle into three plates with three individual bowls of dipping soup. Serve with green parts of green onions, ichimi togarashi pepper on side.