Rinse pork loin to remove residue and pat dry with paper towels. Rub with the mesquite seasoning. Then combine the ground cloves, cinnamon, allspice and sugar and rub onto pork as well. Let sit refrigerated for at least 2 hours or over night.
2Preheat oven to 350 degrees F. Heat oil over medium-high heat in a large saute pan with oven safe handles. Sear pork loin on all sides quickly and then move to roast in oven until fork-tender, about 1 hour and 15 minutes. Remove from oven, transfer pork loin to a cutting board, and let rest 5 minutes.
3In the last 30 minutes of the cooking time for the pork loin make the sauce. Melt the butter over medium heat in a large saute pan with a cover. Add the onion and saute until it becomes translucent. Add the apple juice and pour the sherry over, cover and let cook about 10 to 15 minutes. Whisk the cornstarch into the pan along with mustard powder, salt and pepper. Let cook for a few minutes to let flavors blend, then remove from heat, adjust salt and pepper as needed, and keep covered in a warm place.
Slice pork loin down and transfer to a serving dish. Spoon sauce over the meat and garnish with parsley sprigs(if you have some)