1. Heat oven to 425°F (220°C).
2. Pat pork chops dry; season both sides with salt and pepper. On a sheet pan, toss Brussels, red onion and apple slices with olive oil and a pinch of salt; spread out.
3. Whisk cider, Dijon, brown sugar and rosemary.
4. Nestle chops on the pan and brush generously with the cider glaze. Roast 14–18 minutes, flipping chops midway and glazing again, until pork is 140–145°F and veg is tender. Rest 5 minutes.
5. Spoon any pan juices over the chops to serve.