Carolina Pulled Pork Sandwich

1/4 cup butter
1 1/2 cups chopped onion
3 cloves garlic, chopped
1 tablespoon powdered mustard
1 tablespoon paprika
1 teaspoon ground cinnamon
1 teaspoon cayenne pepper
2 cups catsup
1/4 cup packed dark brown sugar
1/4 cup apple cider vinegar
2 cups water
1 teaspoon salt
1/2 teaspoon ground black pepper
1 tablespoon vegetable oil
1 whole (5 pound) Boston pork butt
12 soft hamburger buns

Melt butter in saucepan. Add onion and garlic; cook until softened, 5 minutes. Add mustard, paprika, cumin and cayenne; cook 1 minute. Add catsup, sugar, vinegar and water; simmer, covered, 30 minutes. Uncover; simmer 30 minutes. Add salt and pepper. This can be made two days ahead, then refrigerated, covered. Before using, simmer 3 minutes.

Preheat oven to 350 degrees F. Heat oil in large ovenproof Dutch oven; add pork; brown for 10 minutes.

Bake, uncovered for 30 minutes. Pour 1 cup of barbecue sauce over pork. Cover pot. Lower heat to 250 degrees F. Bake 3 to 3 1/2 hours, basting meat occasionally, until a thermometer inserted in the middle of the roast registers 170 degrees F to 180 degrees F.

Let cool slightly. Trim off excess fat. Pull meat apart using two forks. Mix pulled meat with remaining barbecue sauce in a large bowl.