Preheat oven to 200˚ C, fan.
Season the pork liberally with salt and pepper on all sides. Using a small sharp knife, make about 10 small holes on the pork. Stuff holes with garlic halves and rosemary. Using a pastry brush, spread Dijon mustard all over the pork.
To make the sauce combine all ingredients, except the chicken broth, in a bowl.
Pour olive oil on the base a large baking pot (clay, ceramic or glass). Add the potatoes and season. Top with the onion slices and pour over half of the sauce. Position the pork o top of the onions and gently pour over the remaining sauce. Slice the whole orange in quarters and place around the pork. Pour over the chicken broth.
Cover the pot with a wet parchment paper, then cover tightly with foil and the pot lid.
Reduce oven temperature to 170˚ C, fan. Roast pork for 2 ½ hours. Uncover pot, and increase oven temperature to 200˚ C. Return uncovered pot to the oven and roast for 30 minutes longer, basting with the pan juices.
Rest meat for 15 minutes, then slice and serve with the potatoes, onions and pan juices.