What is the difference between a pork loin and a pork tenderloin? I have been buying pork tenderloins that are about 11-12 inches long and about as thick as my wrist. I cut them in about 4-5 pieces that gives me a piece about 3 inches. I then butterfly cut it, spread it and pound it out to an oval size at least double the length of a bun and slightly larger in the other direction.
I use a hammer. If you read through this thread I believe I posted a picture of it. However, you can buy a more refined tool with a smooth side and bumpy side at Target that works fine. Use the smooth side. The bumpy side might chew up the tenderloin because you do flatten it out quite a bit.
For frying (at home) I use a Philips HD6161 stainless steel deep fryer. You can Google that to see what it is. I have used an iron skillet but like Janicks said you have to be very careful. Janicks says fry at 350 degrees. With a deep fryer you can pretty much set it. With a skillet it is a guess. I have been frying at the maximum 375 degrees for no more than 3 minutes with good results. It seems the hotter you fry the less greasy the breading.
For breading I have used the saltines that Janicks uses and Brickyard Crossing uses in Speedway. That's the authority. I have also tried commercial bread crumbs and I have tried combinations. I have also used a little corn meal mixed in.
For marinading, buttermilk, flour and egg is the classic way. Another twist I tried was a good hoppy ale prior to the classic way.
Its fun and the farther you are away from the heartland the more you will impress your friends that probably have never experienced a deep fried pork tenderloin sandwich.