Just a heads up, this is more of a method of cooking rather than a specific recipe, so forgive me if this is the wrong section. EDIT: I see there is a meat section which makes more sense for this than recipes, so I went ahead and move it. Ahem, anyway… 
Also, I do not have access to a pit right now, so I am going off of memory from long ago. But hopefully this can spark some ideas for others to try.
To start off, you need a deep pit. The method here uses an underground pit. Typically I see these made by sinking a large steel or concrete pipe into the ground to form the pit. Normally they are about 3 feet or so in diameter and about 4 feet deep. You could also build one with poured concrete or concrete block, and line it with fire brick. You will also need a heavy steel lid to cover the pit that fits nice and flush to the top of your pipe or brick.
First, you need to build a nice hot fire. The last time I did this I used about 8-10 good sized oak logs. Always use hardwoods for this, not soft. The specific type doesn’t matter as we aren’t smoking the meat, just using it for heat. Build your fire and let it burn hot. It will take hours to get down to a nice bed of hot coals.
Now for the meat. I believe last time I did this I used a chuck roast. You can use any large chunk of meat, from beef, to pork, turkey, whatever you want. But I like beef. Cut the meat into large chunks, and season with salt and pepper, or your favorite rub. You could also do the entire thing without cutting it up, but I like to get more seasoning everywhere.
Next, you need to wrap the meat in many layers of heavy duty aluminum foil. Be sure to over lap the seams, and keep the bottom portion solid with no openings so the juices don’t run out. I have also seen this done where you put the meat into a plastic oven bag and then wrap that in the foil, but foil alone should also work.
Now you need to put the wrapped meat into a burlap sack that has been soaking in water. This is very important so you don’t end up with a chunk of charcoal. I usually soak the burlap for a couple of hours. Wrap the whole thing in heavy tie wire, the kind that is used to tie rebar (or rerod as some people call it). You can find this at most big box home centers. Put a loop on the tie wire on top so you have something to hook onto to grab the meat with.
After the fire is down to coals, lower the meat in and set it right on the coals, and cover it with the lid. This next part is critical. You must cover the entire thing with dirt, with zero openings anywhere for air to get in. It’s also a good idea to wet the dirt to seal it up. You can also cover it in dirt, soak it, put down a tarp, cover that in more dirt, and soak it again. If just needs to be well sealed. If you don’t, you will again discover your meat burnt to a crisp. The idea is for the coals to extinguish, and you use the heat built up in the pipe/brick and surrounding dirt to cook the meat.
Finally, you wait. Anywhere from 8-12 hours is good depending on how much meat you do. I think the last time I did it I waited 10 hours and had 20 lbs of meat. You can easily do over 100 lbs depending on the size of your pit, so this is a great way to cook bulk meat for a party.
After the time is up, remove all the dirt, and open the lid. Be careful as the lid could still be hot. The one I used had a piece of rebar welded to the lid to give you something to hook into and lift it with a pole with a hook rather than touching it. Last thing is to use your hook to lift the meat out, undo the tie wire, and expose the meat. The meat will be super tender and just fall apart. I like to shred the meat, then transfer it into a container, and pour all those yummy juices left in the foil into the container.
The result is some of the most flavorful and tasty beef I’ve ever had in my life. I cannot wait to build a pit and start doing this again. Unfortunately I’m in a rental house, and I don’t know how the landlord will feel about me digging a big hole in the backyard. I guess it couldn’t hurt to ask. 