Preheat oven to 350 degrees F. Rub the Hidden Valley® Original Ranch® Salad Dressing and Seasoning Mix all over the pork loin. Season with the pepper. Let rest at room temperature for up to 2 hours. Add 2 tablespoons oil to a large (12-inch) ovenproof saute pan and, just when the oil begins to swirl, add the pork loin and sear on all sides until golden, about 3 minutes each side. Remove to a plate. Toss the potatoes in the oil left in the pan. In a small bowl, mix together the brown sugar and remaining 2 tablespoons oil. Rub into the pork on all sides. Then place back into the pan and into the oven and surround with the sweet potatoes. Bake, stirring the sweet potatoes once or twice, until the pork is cooked through and the sweet potatoes are softened, about 40 minutes for medium. Remove the meat to a cutting board and let rest for 15 minutes before slicing. Skim off the excess fat from the pan. Toss the sweet potatoes with the Hidden Valley® Original Ranch® Salad Dressing. Keep warm until ready to serve.