Preheat the oven to 350 degrees F (175 degrees C). Spray a large casserole dish or Dutch oven with cooking spray.

Place Dijon mustard in a bowl. Combine brown sugar and flour in a second bowl. Coat pork cubes with Dijon, then toss in brown sugar-flour mixture to coat.

Heat olive oil in a large skillet over medium heat. Cook brown-coated pork cubes on all sides in hot olive oil, about 3 minutes per side. Transfer browned pork into the prepared casserole dish, leaving oil in skillet.

Cook and stir onion and garlic in the hot skillet until onions are soft, about 5 minutes. Stir chicken broth, sherry, sweet potato cubes, black pepper, rosemary, thyme, and salt into onion; bring to a boil. Pour sweet potato mixture over pork and cover casserole dish.

Bake in the preheated oven for 50 minutes; uncover and bake until pork is no longer pink inside and sweet potato cubes are tender, about 20 more minutes.