For garnishes, shell the shrimp, leaving the tail attached, and devein. Wash, pat dry, salt lightly, and lightly dredge in cornstarch (or kuzu starch or arrowroot). Parboil in unsalted water for 2 minutes. Soften the dried wakame seaweed in cold water for 20 minutes. Cut out hard parts and discard, then cut into 1-inch (2 1/2-cm.) lengths. (Professional chefs might treat wakame in a slightly different way to bring out its bright green color and to insure tenderness: swish it in boiling water for 30 seconds then plunge it into a cold bath before leaving it to soak.) Wash and pat dry the mitsuba sprigs.
In a medium-sized soup pot, bring the dashi to a simmer over medium heat. Never boil. Add the miso gradually, dissolve it little by little. Gradually add the soy sauce. Stir and taste. The higher the quality of the dashi, the less soy sauce required.
Warm individual covered lacquer soup bowls by filling with hot water and letting them stand for 1 or 2 minutes. (In lieu of lacquer bowls, use small or medium-sized deep soup bowls or cups on saucers.) Dispose of hot water and wipe bowls dry. Attractively arrange 3 shrimp, 3 shiitake mushrooms, and a small amount of seaweed in each bowl. Ladle in the seasoned stock carefully so that it does not splash and mark the side of the bowl or disturb the arrangement. Fill bowls 3/4 full no more. Add a sprig of mitsuba to each bowl. Serve immediately.