Chill the pork shoulder, fat, grinder parts, and food processor to 32ºF or less. Grind the shoulder through a small die into the chilled food processor bowl. Grind the fat into a separate chilled bowl and refrigerate.
Add the salt, curing salt, garlic paste, dextrose, mace, coriander, cinnamon, cayenne, and half of the ice to the meat. Blend the meat in the food processor to a smooth pink paste with a temperature of 42-45ºF. Push down the meat on the sides of bowl until fully incorporated and continue processing. Do not let the temperature of the mixture exceed 45ºF.
Once the meat is smooth add the remaining ice and the chilled ground fat to the food processor bowl. Blend the fat into the meat until a smooth paste is formed, pushing down the sides from time to time. Stop the machine when the paste reaches 58˚F-62˚F and transfer to a bowl. Add the meat mixture and fold in the pork jowl, pistachios, and peppercorns. Stuff the meat into a clean beef bung and pack it tightly so that there are no air pockets. Secure the end with a strong knot and create a loop.
Place the mortadella in a large pot and cover with cold water. Lay a plate over the mortadella to keep it submerged while cooking. Slowly heat the water to 160ºF and hold it there for the duration of the cooking. Cook for 4 hours or until the mortadella reaches an internal temperature of 155 ºF. Check the temperature every 45 minutes to monitor the cooking. When the mortadella reaches 155ºF, immediately plunge into an ice bath. Transfer to a refrigerator and serve after 2 days.