Further musings on the Filet-o-Fish

The bun is steamed, which probably accounts for its family resemblance to the steamed bun of dim sum. The history is of interest: The FOF has Catholic roots, and won a place on the McDonald's menu against a competing vegetarian sandwich that featured a slice of pineapple in place of the fish (the Hula Burger!).

I've always found it somewhat anomalous that such an exquisitely symmetrical sandwich should have only a half-slice of American cheese, rather than a full square to nest right below the fried filet. But as the purpose of the cheese is more adhesive than gustatory, a half-slice is probably sufficient. 

From Wikipedia:

The sandwich was invented in 1962 by Lou Groen, a McDonald's franchise owner in Cincinnati; his store was in a predominantly Roman Catholic neighborhood, which led to falling hamburger sales on Fridays resulting from the Roman Catholic practice of abstaining from meat on Fridays...

The sandwich was the first non-hamburger menu item brought in by new McDonald's company owner Ray Kroc. Kroc made a deal with Groen: they would sell two non-meat sandwiches on a Friday, Kroc's own Hula Burger (grilled pineapple with cheese on a cold bun) and the Filet-O-Fish, and whichever sold the most would be added to the permanent menu. The Filet-O-Fish "won hands down" and was added to menus throughout 1963 until reaching nationwide status in 1965.