Partially freeze beef; trim separable fat. Thinly slice the meat across the grain into bite-size strips. Set aside.
In a bowl pour boiling water over cellophane noodles to cover; let stand 10 minutes. Drain. With kitchen shears, cut noodles into 2-inch lengths.
In a mixing bowl stir together beef broth, sake or dry sherry, soy sauce, and 1/4 teaspoon pepper; set aside.
Spray a large skillet or wok with nonstick spray coating. Preheat over medium heat. Add bok choy and green onions; stir-fry 2 to 3 minutes or until vegetables are crisp-tender. Remove from skillet. Add bean sprouts, bamboo shoots, and mushrooms; stir-fry 1 to 2 minutes or until mushrooms are tender. Remove vegetable mixture from skillet.
Add oil to hot skillet; swirl to coat. Add beef; stir-fry 2 to 3 minutes or until beef is cooked through.
Add tofu and broth mixture to skillet. Cook and stir until bubbly. Return all vegetables to skillet. Add noodles. Cover and cook 2 to 3 minutes or until heated through. Makes 4 servings.