Peel 1 pound of sweet potatoes and cut into large chunks. Spread the potatoes, onions and garlic over the bottom of a large slow cooker. Season the pork on all sides with salt, then place the pork on top of the vegetables.
In a large bowl, mix together the tomatoes and their juices, along with the chipotles, adobo, Worcestershire, oregano and 2 teaspoons salt. Pour the mixture over the pork, cover and set the slow cooker on high and the timer for 6 hours.
After 6 hours, carefully remove the meat to a platter and once it's cool enough to handle, discard any fat and shred the meat. Scrape the sauce and vegetables into a food processor and blender (you may need to do this in several batches depending on the size of the container) and process to blend the vegetables into the sauce. Taste and add more salt if necessary. Measure 1 1/2 pounds of the shredded pork plus 3 cups of the sauce and place in a resealable bag and freeze. This is the pork you'll use to make the Shredded Pork Tortas.
Peel the remaining sweet potatoes and cut into 1/4-inch slices. Place them in a large pot of heavily salted cold water. Bring the potatoes to a boil and cook for 3 to 4 minutes. The potatoes should be barely tender. Drain and cool.
Once the sauce has cooled to room temperature, spread 1 cup of the blended sauce into the bottom of a 13 x 9-inch oven safe casserole dish, then cover with 8 tortillas. Next, top with half of the shredded pork and half of the sliced sweet potatoes. Spread on one-third of the remaining sauce, then sprinkle on one-third of the cheese. Repeat the same method for the next layer. For the last layer, the sequence is tortillas, sauce and then top with cheese.
If you're baking right away, set the casserole dish onto a rimmed baking sheet and place on the center rack of a preheated 350 degree oven. Bake for 60 to 70 minutes or until the center is piping hot. If the cheese is getting too brown, loosely cover with foil. Remove from the oven, tent with foil. Let stand for 15 minutes before serving.
If you're preparing this boudin for a future dinner, wrap well and place in the freezer. The night before you're ready to serve, move the boudin to the refrigerator to defrost. Bake in a preheated 350 degree oven, it will take about 90 minutes to bake.