Reduce heat to medium-high and add onion to the pan. Cook, stirring often, until it starts to soften and brown, 2 to 3 minutes. Add apple and cook, stirring often, until tender, 3 to 5 minutes. Stir in the remaining broth, cider (or juice), mustard, thyme and the cornstarch mixture. Bring to a boil, stirring, until thickened and glossy, about 1 minute. Return the chops to the pan and heat through. Serve immediately.