Add shallot to the pan and cook, stirring constantly, until softened, 30 seconds to 1 minute. Add wine and bring to a boil, stirring constantly. Boil until reduced to about 2 tablespoons, 2 to 3 minutes. Whisk cornstarch and vinegar in a small bowl; whisk into the sauce. Cook, stirring, until thickened and glossy, about 30 seconds. Remove from the heat and stir in jelly, sugar (if using), mustard and any accumulated juices from the pork. Serve the pork with the sauce.