The third and final version of the story took place in Two Rivers, Wisconsin, in 1881. The supposed inventor was a man named Ed Berners, who, like our other inventors, was the owner of a soda fountain. One day a customer by the name of George Hallauer requested a dish of ice cream topped with the syrup used to make sodas. Soon after Berners added it to his menu and charged a nickel. Meanwhile a competitor soda owner caught on to this new treat, but because he thought the price was too cheap, he only served it on Sundays. Hence, it was called the “Ice Cream Sunday”. Before long, it was doing so well, he decided to serve it everyday and thus the name changed to “sundae”.
I learned about this fact from: http://inventors.about.com/od/foodrelatedinventions/a/Sundae.htm