Chef Fred Bangerter is believed to have created the dressing around 1935.
[1] The dressing was also credited to the head waiter of that era named Harry Amos.
According to legend, Mayfair salad dressing is made from an oil (such as corn or canola) and whole egg base seasoned with anchovies, garlic, prepared mustard (horseradish mustard may be used), celery, onion, champagne, and black peppercorns.
The dressing was the signature dish at the historic Nantucket Cove restaurant in St. Louis, whence the proprietor had purchased the tightly guarded secret recipe from the Mayfair hotel iteself.
While the original recipe remains a secret, there are many versions of "Mayfair dressing" on the menu in present day St. Louis restaurants.