Long, slow braising creates succulent and tender short ribs, flavored in this recipe with Chinese Five-Spice Powder, orange juice, and both fresh and ground fennel. The flavor combination works well with veal or lamb shanks as well. If you can't find ground fennel in your market, grind fennel seeds to a fine powder in a coffee or spice grinder.
Dry the short ribs with paper towels and spread them on a baking tray. Season liberally with the salt and pepper on all sides.
Combine the Chinese Five-Spice and dry mustard powders and spread the mixture on a plate. Dip each rib into the spice mixture, lightly coating each side.
Heat about 1/4 cup of the oil in a large Dutch oven over medium-high heat. When the oil is hot, add some of the short ribs to the pan. Don't crowd the meat. Brown the ribs, turning them with tongs to brown all surfaces. Remove the browned ribs to a baking tray and repeat with the remaining meat. Add more oil to the pan as needed.
Wipe out the Dutch oven with paper towels. Add 1/3 cup of oil to the pan and heat over medium-high heat. Add the onions, fennel, and carrots, and cook, stirring frequently, until the vegetables are tender and lightly caramelized, 10 to 15 minutes. Add the garlic and cook over medium heat for 2 or 3 minutes, stirring constantly.
Add the tomatoes and orange juice to the pan and bring to the start of a simmer. Add the short ribs, cover, and reduce the heat to medium-low. Maintain a slow simmer, turning the ribs once or twice, and cook until tender, 2 to 2-1/2 hours.
Transfer the ribs to a platter with tongs and cover with aluminum foil. Increase the heat to high and bring the sauce in the Dutch oven to a boil. Cook to reduce the liquid and concentrate the sauce to the desired consistency, about 10 minutes. Remove from the heat and stir in the ground fennel and orange zest. Pour the sauce over the ribs and serve immediately.