16-pound boneless pork shouldertrimmed of excess fat and tied
In a small food processor combine the garlic, anchovies, rosemary, salt and pepper. Add the olive oil and process until it forms a paste, scraping down the sides. Remove the blade and use a fork or spoon to stir in the mustard. Rub the paste all over the pork shoulder, loosely cover it with plastic wrap, and refrigerate from 2 to 24 hours.
Preheat the oven to 450°F and bring the pork to room temperature while the oven heats. Place the pork in a shallow roasting pan and roast, uncovered, for 30 minutes, until the top starts to brown a bit. Turn the heat down to 250°F and continue to cook, uncovered, for 6 to 8 hours until the middle of the roast registers 180°F. on an internal thermometer, and as you slide the thermometer in you can feel that the meat is very tender throughout. If there are juices in the pan (and I have found that sometimes there are and sometimes none) pour off the juices from the pan into a heatproof container, like a Pyrex measuring cup. Place this in the fridge, where the fat will rise to the top, while the meat rests.
When the meat is cooked, if you think that the outside of the roast could use a bit more crust/brownness, turn the heat back up to 450°F and let it cook for another 15 to 20 minutes, to give the outside a bit more of a crunchy texture.
Remove from the oven and let sit for about 20 minutes. Spoon the fat off the reserved juices in the fridge and pour the cooking juices into a serving pitcher or bowl (warm it a bit in the microwave or in a small pot if you like). Slice the pork as thinly or thickly as you like, knowing the meat will fall apart at least slightly. Sprinkle the sliced meat with a bit of salt before serving, and pass the pan juices on the side to drizzle over.
You can also make this recipe and others like it with a pork butt roast or Boston Butt pork roast, which are actually also from the shoulder area, a little further up, but essentially a similar cut of meat.