Chop chicken very fine, or put in a blender or food processor. Soak chopped chicken in 1/2°C of chicken stock.
Beat egg whites stiff then gently fold in cornstarch, chicken, and 1 tsp of salt. Set aside.
Cook spinach in a small amount of boiling water, drain well then squeeze out water and chop very fine.
Heat oil in a wok over medium-high heat. Stir-fry spinach for 30 seconds. Pour remaining 4°C chicken stock and sherry over spinach and bring to a boil. Add chicken mixture and bring to a boil, stirring rapidly.
Season with 1 teaspoons salt. Thicken with dissolved cornstarch.