Pork Rib Roast with Apples, Fennel, and Potatoes

Score rib-roast fat cap with the tip of a paring knife in opposite directions, to create a 1/2-inch crosshatch. Prick roast all over with knife tip at approximately 1-inch intervals, about 1 inch deep. Generously season with salt and pepper, rubbing it into meat with your hands. In a bowl, stir together mustard, soy sauce, chopped rosemary, and coriander and fennel seeds.

Rub mixture all over pork. Let stand at room temperature at least 1 hour and up to 2 hours, or loosely cover and refrigerate up to 1 day (return to room temperature at least 1 hour before roasting).

Preheat oven to 450°F. In a saucepan, combine potatoes and enough cold water to fully submerge them. Bring to a boil. Season with 1 tablespoon salt and boil until tender and easily pierced with the tip of a knife, 12 to 15 minutes. Drain and let cool slightly. Using a flattened palm or the bottom of a measuring cup, flatten potatoes slightly (but keep them intact).

Transfer potatoes to a large roasting pan with onions and fennel. Toss with 2 tablespoons oil, season with salt and pepper, and spread in a single layer. Scatter rosemary sprigs over vegetables. Place marinated pork in center of pan, atop vegetables.

Roast 15 minutes. Meanwhile, core and quarter apples and toss with remaining 1 tablespoon oil; season with salt and pepper. Reduce oven temperature to 350°F. Scatter apples into pan and continue cooking until vegetables are tender and a thermometer inserted in center of roast registers at least 135°F, 1 hour, 15 minutes to 1 hour, 45 minutes more, depending on size.

Transfer pork to a carving board, loosely cover, and let stand 20 minutes; discard rosemary. Turn oven off and return vegetables to oven to keep warm. Carve pork and serve with vegetables and more mustard.