Mad As a Hatter

I might not be quite that mad,but sometimes my mind goes to strange places...for instance,I have always wondered how a Pork Pie hat got its name. It was one of those questions no one seemed to know the answer to and I never seemed to be in the right place at the right time to find an answer until today. Its name has a literal meaning,the Jazz and Blues musicians in New Orleans (often seen with this type hat) were food sellers by day which gave them access to pie tins. They would take old battered dress hats,trim off the damaged outer brim and re-block the hats over pie tins. I'm still not entirely clear on where the pork portion of the name comes into play,but one theory is they resembled a pork pie. If anyone knows the complete answer please let me know!