Preheat all oxen to 300°F. Lightly oil a large baking pan.

Place the pork shoulder in the prepared pan and rub  with the red pepper flakes, salt, black pepper, and mustard seed. Pour the water and the vinegar over and around the pork. Scatter the onions and the bell pepper over and around the meat. Cover with aluminum foil and roast in the oven for 4 hours.

Remove the foil and continue to roast until an instant-read meat thermometer inserted into the thickest part off the pork away from the bone registers 180°F and the juices run clear, about 1 hour longer. Remove the pork from the pan and let stand for 1 hour. Using 2 forks, shred the pork by steadying the pork shoulder with 1 fork and pulling the meat away with the other, discarding any fat as you shred. Place the pork in a bowl. Using a slotted spoon, lift the roasted vegetables from the baking pan and ladle over the pork, then mix well.

Meanwhile, make the sauce: In a saucepan over medium heat, melt the butter. Stir in the onions and the garlic and cook, stirring occasionally, until the onions are soft and beginning to brown, about 10 minutes. Add the puréed tomatoes, tomato paste, peach preserves, mustard, bourbon, honey, brown sugar, vinegar, Worcestershire sauce,Tabasco sauce, salt, and black pepper. Bring to a boil, then reduce the heat to very low and simmer gently, uncovered, stirring occasionally to prevent sticking, until the sauce is very dark and thick, about 2 hours. Stir in the rosemary and cook for 10 minutes to blend the flavors.

Remove from the heat and let cool for 15 minutes.

Mix half of the sauce with the shredded pork.

Mound on a large serving platter with the sandwich buns and the pickle slices on the side. Pass the remaining sauce at the table. Diners make their own sandwiches, topping them with pickle slices.