Cook the noodles and drain according to the package instructions. Rinse with cold water then place in the fridge to chill while you prepare the rest of the items.
Pour boiling water over the dried mushrooms and let them soak for 30-45 minutes, until softened.
Season the pork belly with the salt and cook it in a skillet over medium heat until brown on broth sides (it will be crisped when done).
Squeeze the liquid from the mushrooms and slice thinly for serving (discard the stems). Reserve ¼ cup of the mushroom liquid.
Combine the stock, bonito flakes, ginger, miso, mirin, ¼ cup mushroom liquid and soy sauce in a pot and bring to a simmer for 5 minutes.
Remove from heat and strain. Mix in the sesame oil and vinegar.
Let cool to room temperature for serving (can place in the fridge to cool it faster).
Serve the broth in a bowl on the side of a plate of noodles, eggs, green onions and crisped pork belly.