Put the pork shoulder in the freezer for 15 minutes. This makes it easier to cut into thin slices. While the pork is firming up, prepare the marinade.
Cook the chiles in a large skillet over medium high heat for 5 minutes. They should be puffing up, pliable, browning in spots, and very aromatic.
Add the chicken stock to the skillet and then pour the chiles and stock into a bowl. Place a plate, towl, or plastic wrap over the top and set aside.
Dry the saucepan and add the vegetable oil. Heat on medium high until the oil is shimmering. Add the oregano, cumin, and achiote, stirring frequently for about 30 seconds. The spices should smell aromatic but not browned.
Add the chipotle chile and adobo sauce and cook for 30 more seconds.
Stir in the vinegar, salt, and sugar and remove from heat.
Scrape the contents of the skillet into a food processor or blender. Toss in the garlic cloves and pour the chiles and their soaking liquid and blend on high speed until completely smooth. Set aside.
Take the pork out of the freezer and slice it as thinly as possible.
Place one slice of pork into a heavy duty ziplock bag and pound with a meat pounder or the bottom of a heavy skillet until it is less than ¼ of an inch thick. Place in a large bowl and repeat with the rest of the pork slices.
Add the marinade to the bowl and toss with your hands (wear disposable rubber gloves to protect your hands from the heat of the chilies). Make sure every slice of pork is evenly coated.
Wrap tightly in plastic wrap or transfer to a ziplock bag and marinate for at least 4 hours or up to 36.
When the meat is finished marinating, preheat the oven to 275 degrees Fahrenheit.
Cut two circular rounds off the top and bottom of the peeled pineapple and set aside. Core the rest of the pineapple and cut into quarters lengthwise.
Take a skewer and make sure that it can stand up straight in a large dutch oven with the lid on. Cut it down to size if it is too tall.
Place one of the pineapple round slices on the skewer to form a base. Begin adding layers of the pork on top of the pineapple. At the very top of the pork slices, add the second pineapple slice.
Cover with the lid and cook in the oven for 4 hours.
Remove from the oven and take the lid off. Place pineapple quarters in the dutch oven and flip them so that all the sides are covered in fat.
Put back in the oven and cook uncovered for 25 minutes, until the pineapple is tender.
Carefully remove the skewered pork from the dutch oven and place on a cutting board. Let the meat rest for 10 minutes (or until the internal temperature reaches 120 degrees).
Cut the pineapple into large chunks. Dice and mince the onion and cilantro. Cut the limes into wedges, and put the salsa in a serving bowl.
Warm the tortillas in the microwave, oven, or skillet, whichever method you prefer.
Pour all the fat and juices that collected in the dutch oven into a measuring glass or bowl and set aside.
Using a chef’s knife or slicing knife, thinly slice the meat, creating fine shavings of meat.
Heat 1 tablespoon of reserved juices in a large skillet over medium high heat. Add the meat and cook, stirring occasionally, until the meat crisps and deeply browns in spots.
Add the rest of the reserved drippings and toss to combine. Cook until the juices are reduced to a moist glaze. Transfer to a serving bowl.
Serve the meat and pineapple with warm tortillas, onions, fresh cilantro, salsa, and lime wedges.