Place a large 8-10 quart braising pot/Dutch oven on the stove and turn the heat on medium-high. As the pot is heating up, season the pork shoulder chunks with kosher salt (be liberal with the amount of salt you use!). Add oil to pot (it should immediately start to shimmer) and add the seasoned pork chunks. Allow the pork to brown on all sides, about 2-3 minutes per side. Using tongs, transfer the pork to a bowl and set aside.
Reduce the heat to medium-low. Add the shallots and cook until translucent (but not browned!), about 5-7 minutes. Add carrots and celery, cook for an additional 2-3 minutes, stirring frequently. Add cocoa powder and stir to make sure it is distributed evenly throughout the cooked vegetables. Increase the heat to medium-high, add the Guinness and bring to a boil (about 2 minutes). Add the chicken broth, bay leaf and seared pork chunks and turn the heat off. Stir and cover tightly with fitted lid or aluminum foil.
Place covered braising pot/Dutch oven in preheated oven for 3 ½-4 hours, until the pork is fork-tender and pulls apart easily.
Just as you are about to remove the sauce from the oven, fill a large pot with water to cook your pasta in. Place the pot of water on the stove, add salt to the water and bring to a boil.
Remove the pot from the oven and place on the stove. Turn the oven off and turn the stove onto the lowest setting. Remove the bay leaf and discard. Remove the pork shoulder from the pot and shred the chunks by pulling them apart with two forks. Place the shredded pork back into the pot. Stir and taste the sauce (add additional salt if needed).
Add your paccheri to the boiling pot of water, cook as directed on package. Reserve 1 cup of pasta water and then strain pasta when done.
Turn off heat beneath ragu. Add cooked paccheri, ½ cup of reserved pasta water, 1 Tbsp unsalted butter and ¼ cup of grated Parmigiano-Reggiano. Stir to coat. The final sauce should not be soupy, rather it should coat the pasta evenly.
Serve on plates and garnish with additional freshly grated Parmigiano-Reggiano. Enjoy!