Frozen custard was invented in Coney Island, New York in 1919, when ice cream vendors Archie and Elton Kohr found that adding egg yolks to ice cream created a smoother texture and helped the ice cream stay cold longer. In their first weekend on the boardwalk, they sold 18,460 cones.
The 1933 Worlds Fair in Chicago
A frozen custard stand at the 1933 World's Fair in Chicago introduced the dessert to a wider audience. Following the fair, the dessert's popularity spread throughout the Midwest; Milwaukee, Wisconsin, in particular, became known as the "unofficial frozen custard capital of the world".