A "Fatty" is basically BBQ meatloaf. They can be made many different ways and customized any way you can think of.
The basic fatty is sausage in the middle, surrounded by cheese, surrounded by meat, surrounded by bacon.
They can be very impressive at your party when you take it out and slice it up for your guests, and are super easy to make. Note the smoke ring just under the bacon layer on my fatty on the left. The smoke can go through that thin layer of bacon and impart a great extra flavor.
Start with your bacon wrap, first. Be sure to lay down a piece of parchment paper, first, to make it easy to roll up when done. It's easy to make, just layer it one strip at a time. If you don't want to make the weave like I did, then you can also just lay strips down over the finished roll. The wrap holds together much better, however.
Next, lay down your choice of ground meat. Be sure to season it! I mix the meat with my rub in a bowl, first. I have used ground beef, ground turkey, ground sausage, all of it works.
Then, lay down your cheese layer. Tillamook sharp cheddar is my favorite, but really you can't go wrong here, just use whatever you like.
On top of the cheese, I then add a large kielbasa style sausage. This can also be whatever you want. Go nuts.
Now, roll it up and tuck in the ends. Sprinkle BBQ rub on the outside, then wrap it tight in plastic and put it in the fridge overnight until you're ready to smoke.
Smoke at 225-250 for about 2 or 3 hours. It's done when you stick a probe into the ground meat section (NOT the center) and you get the safe temperature for that meat (135 for beef, 155 for poultry) The sausage is typically safe to eat out of the bag, so be careful not to probe that by mistake.
One time, I went with an Italian theme and went with ground beef seasoned with typical pizza seasoning, and then used mozzarella cheese, and then used thick pepperoni in the middle. That worked out just fine.