(NationalGeographic) - Arkansas to deliver what he calls an “anti-cookbook cookbook.” The former chef, who started in the restaurant business as an 11-year-old dishwasher at a fast food chicken shack near Chicago, ate his way across the 50 states for his new book, The Mad Feast: An Ecstatic Tour Through America’s Food. American cuisine, he discovered, is as varied as its ethnic make-up.

Speaking from a parking lot in Michigan during his book tour, Frank explains why bagels have a hole in them; how Florida sponge fishermen may have created Key Lime Pie; and how rat meat, stewed in red wine, was once a delicacy in medieval France.

Many states have official dishes they claim as unique. Give us a few examples – and explain how a dish becomes “official.”

I wouldn’t necessarily call any of these “official,” but they are certainly typical of the U.S. states to which they apply. For instance, for the state of Minnesota, I chose this strange concoction called “hot dish.” It was originally made from whatever was around during lean times, in Lutheran Church basements, in order to feed congregations with a high fat, stick-to-your-ribs dish. It has no official recipe or rules beyond economic and gustatory desperation. [Laughs] One kind of hot dish is made with hamburger meat, mashed potatoes, string beans, and cream of mushroom soup, with La Choy fried onion. Another version uses canned tuna, Kraft macaroni and cheese, canned peas or corn, topped with either crushed potato chips, shoestring potatoes, or even corn flakes. It’s pretty revolting. [Laughs] The cream of mushroom soup binder became known in Minnesota as “Lutheran Binder.” Today there are chefs in downtown St. Paul-Minneapolis who are attempting to rescue “hot dish” from mundanity and Lutheran Church basements and situate it within the realm of the gourmet.

The U.S. is a huge country with great climatic, economic and geographical variety. How is this reflected in local cuisines?

I covered all 50 states for my research, and the local cuisine is ridiculously varied and affected by numerous immigrant cultures. A lot of the foodstuffs come via a diaspora and, like identity in general in the U.S., there isn’t a single narrative. For instance, some food historians believe that key lime pie was invented by Florida Keys sponge fishermen in the late 1800s because they were bound to their boats for days on end and needed a high fat, high protein, high sugar diet. They brought in canned condensed milk and eggs and pre-soured it with key limes. But when I did an interview with a radio show in Miami, they took major issue with the fact that I attributed the invention to sponge fishermen.

In West Virginia, the dish I chose was rat stew. Rat stew was born out of lean times as a result of the collapse of the mining industry. Folks had to turn to emptying their rat traps into stockpots in order to eat meat. The strange thing is that rat meat, in old Bordeaux, France, was seen as a food of the aristocrats. Vintners used to catch rats and throw “rat parties,” where they cooked the rats in this beautiful sauce of red wine, tarragon, and shallots, roasted over a fire made from broken down Bordeaux barrels.