Preheat an oven to 400 degrees F. Stir the hoisin and ketchup together in a large bowl. Season the spare ribs on both sides with salt and pepper.
Cut the rack into individual ribs. Add to the hoisin mixture and toss to coat evenly. Transfer the ribs to a large baking dish, clean the sides of the dish, and cover with aluminum foil. Place the ribs in the oven.
Cook the ribs in the oven for 25 minutes, then remove the foil and continue to cook until the sauce becomes syrupy and the meat is tender, about another 25 minutes. Remove from the oven, pile the ribs on a platter, and serve immediately.