Gently beat the eggs with the salt, sherry, and pepper. Add the crabmeat, celery, black mushrooms, bean sprouts, and onion and mix well.
Heat the oil in a nonstick work or stir-fry pan over medium-high heat until the oil is not smoking. Test by dipping the end of a spatula into the egg mixture and then into the oil; it should sizzle. Add the egg mixture to the hot oil. Let the eggs sit without stirring until the bottom is slightly set but the top is still runny. With a spatula, turn sections of the eggs over. Continue turning the eggs until the mixture is set on both sides. Remove to a serving platter. Serve immediately.
Variation: Serve the Egg Foo Yung with a restaurant-style brown sauce. Make the sauce before cooking the eggs.
Mix together 1 cup homemade Chinese Chicken broth, plus 1/2 teaspoon salt or 1 cup of canned chicken broth, 1/2 teaspoon ketchup, 1 1/2 teaspoons soy sauce, and 2 tablespoons flour, mixed with 2 tablespoons cold water into a smooth paste, in a saucepan. Cook over medium heat, stirring constantly with a wire whisk. Bring to a boil and stir until the sauce is thickened. Simmer 2 minutes to eliminate the raw taste of the flour. Pour the sauce freely over the cooked eggs.