pork loin roast, bone-in, about 5 pounds
1/2 cup chopped onion
2 tablespoons butter or vegetable oil
3/4 cup water
3/4 cup ketchup
1/2 cup cider vinegar
3 tablespoons
brown sugar
1 tablespoon Worcestershire sauce
3/4 teaspoon dried leaf oregano
3/4 teaspoon ground paprika
1/2 teaspoon garlic powder
3/4 teaspoon kosher salt or 1/2 teaspoon table salt
1/4 teaspoon dry mustard
1/8 teaspoon fresh ground black pepper
dash ground cloves

Heat the oven to 325 F.
Line a roasting pan with foil and place a rack in the pan.
Place the pork roast on the rack and roast it in the heated oven for about 25 to 30 minutes per pound, or until it registers at least 145 F on a food thermometer, the minimum safe temperature for pork.
Meanwhile, make the barbecue sauce. Heat the butter or vegetable oil in a medium saucepan over medium-low heat; add the onion and cook until softened and translucent.
Add the water, ketchup, cider vinegar, brown sugar, Worcestershire sauce, oregano, paprika, garlic powder, salt, dry mustard, black pepper, and ground cloves, and mix well.
Bring the sauce mixture to a simmer. Reduce the heat to low and simmer for about 15 to 20 minutes or until the sauce has reduced and thickened somewhat and the flavors are concentrated.
Baste the pork roast with the barbecue sauce several times during the last 30 to 45 minutes of roasting time.
Let the roast rest for 10 to 15 minutes before slicing.