Step 1
Season one 7–9-lb. skinless, bone-in pork shoulder, fat cap trimmed to ¼”, patted dry, all over with kosher salt and freshly ground black pepper (about 1 tsp. salt per pound is a good rule of thumb, so don’t be shy here). Let sit at room temperature at least 30 minutes and up to 2 hours.
Step 2
Preheat oven to 300°. Heat 1 Tbsp. extra-virgin olive oil in a large Dutch oven or other heavy pot over medium-high. Add 1 large onion, unpeeled, quartered, and 1 head of garlic, halved crosswise through the equator, cut sides down, and cook until browned underneath, about 4 minutes. Transfer to a plate.
Step 3
Arrange pork shoulder, fat side down, in same pot and cook, undisturbed, until browned underneath, about 5 minutes. Carefully turn pork over by rolling away from you to avoid spattering and cook until browned underneath, about 5 minutes.
Step 4
Tuck onion, garlic, and 1 large sprig rosemary around pork (fat side should be up at this point). Add 2 cups red wine, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, ½ tsp. crushed red pepper flakes, and 2 cups water. Cover pot; transfer to oven. Braise 3–3½ hours (depending on the size of your shoulder; go the full time if it’s 9 lb.). Uncover pot and roast pork until meat shreds easily with a fork, about 2 hours.
Step 5
Meanwhile, cut 1 large orange in half and squeeze juice into a cold small saucepan (you should have about ⅓ cup); thinly slice remaining 1 large orange into rounds. Add 1 cup orange marmalade (one 12-oz. jar), ½ cup sherry vinegar or red wine vinegar, a pinch of salt, and remaining ¼ tsp. crushed red pepper flakes to orange juice in pan, set over medium-high heat, and cook, stirring and scraping down sides of pot occasionally with a heatproof rubber spatula, until thickened and syrupy, 7–9 minutes. Set glaze aside (it will continue to thicken as it cools; reheat before using if too thick).
Step 6
Spoon or brush top of pork (any parts you can see above braising liquid) with about a third to half of the glaze. Tuck orange slices around pork. Roast until crust on pork is sticky, 15–20 minutes.
Step 7
Carefully transfer pork to a platter and spoon remaining glaze over. Tuck orange slices in pot around pork along with a few fresh rosemary sprigs. Transfer juices from pot to a small bowl to spoon over individual servings if desired.
