Follow the steps for recipe "Japanese Kelp Stock", which is in the dependent recipes section to the right.
Drain the mushrooms, reserving 2 cups of the soaking liquid. Discard the stems and quarter the caps. In a large pot, combine the kelp stock, mushroom liquid, soy sauce, mirin, and shiitakesBring to a boil over high heat. Reduce the heat to low and simmer, covered, until ready to serve.
MAKING THE NOODLES
Bring a medium pot of water to a boil over high heat. Cook the fresh udon noodles, untangling them until separated and warmed, about 10 seconds (or boil the dried udon for about 5 minutes). Drain and divide among large soup bowls.
Add the chrysanthemum leaves to the pot containing the broth, and when just wilted, remove from the heat.
Ladle enough broth into each bowl to cover the noodles, adding a few chrysanthemum leaves and mushrooms.
Garnish with ginger, and sprinkle lightly with sesame seeds and togarashi if desired.