COMBINE broth, soy sauce, sherry, ginger and onions in medium saucepan or fondue pot. Bring to boil on medium-high heat. Reduce heat to medium-low; simmer 15 min. Meanwhile, mix mayonnaise and dressing; set aside. Cut steak into 1/8-inch-thick slices and mushrooms into 1/4-inch-thick slices. Arrange on platter.

TRANSFER hot broth to fondue pot if not already in fondue pot; place over heat source. Return broth to boil. Insert meat and mushrooms on fondue sticks; place in hot broth mixture. Cook 3 to 4 min. or until meat is cooked through and mushrooms are tender, adjusting heat as necessary for the broth to maintain a constant low rolling boil.

SERVE with the mayonnaise mixture.