Step 1Combine 1 tablespoon soy sauce, 1 tablespoon mirin, 1 tablespoon Sherry, 1 tablespoon garlic and cornstarch in medium bowl. Add beef and stir well. Set aside.
Step 2Combine remaining soy sauce, mirin, Sherry and sesame oil and sugar in small bowl. Set aside.
Step 3Heat peanut oil in a large wok or skillet over high heat. Add ginger and remaining garlic and cook until very fragrant, about 2 minutes. Add mushrooms and cook 2 minutes more. Add reserved beef and snow peas and cook, stirring, until beef is no longer pink, about 3 minutes. Add sauce mixture and cook, stirring, until sauce thickens slightly, about 1 minute.
Step 4Serve ginger beef in bowl, topped with peanuts, with lettuce on side. Wrap some of beef in leaf and eat with fingers.