Combine the roux, salt, and peppers in a shallow dish. Meanwhile, heat the oil in a large, heavy skillet. Dredge pork in seasoned roux and fry, in two batches, over medium-high heat until browned on both sides. Remove pork and keep warm. Pour off any remaining oil in pan. Add wine and scrape up any brown particles that have adhered to the pan. Add mustard, and plum sauce and stir to combine. Return pork to pan, cover, and simmer, turning once, until pork is tender and glazed, about 10 minutes.