Place Shitake mushrooms in medium-size bowl and pour boiling water over. Set aside for 10 minutes to soften.
Cut off stems and discard. Slice mushroom caps 3/4-inch thick and set aside.
Stir together the egg white and 1 tablespoon cornstarch till smooth.
Add diced chicken and mix till completely coated. Set aside till ready to cook.
Combine 1 tablespoon cornstarch, 2 tablespoons water, chicken broth, 1/2 teaspoon salt, pepper, and soy sauce. Set aside.
Heat oil in wok over high heat.
Add ginger, garlic and white part of scallion, stir-frying for thirty seconds.
Add chicken and continue to stir fry, separating the pieces as they cook, till the chicken is completely white.
Add mushrooms, snap peas and sherry, tossing with chicken.
Add chicken broth mixture and stir-fry sauce till hot and thick.
Sprinkle walnuts over and stir to combine.
Transfer to platter and garnish with reserved chopped green scallion. Serve with hot rice.