Preheat the oven to 350 degrees . Heat a large Dutch oven over medium. Season the meat with salt and pepper and cook until browned on all sides, 5 to 6 minutes; transfer to a plate.
Add the next 4 ingredients; season. Cook, stirring, 3 minutes. Add the wine; bring to a boil. Cook until the wine reduces, 10 minutes. Add the stock and rosemary; bring to a boil.
Add the meat, bone side up, and the juices from the plate. Cover; transfer to the oven. Cook until the meat is fork-tender, about 2 1/2 hours.
In a small nonstick skillet, heat 1 tbsp. oil over medium. Add the potatoes; season generously. Using a spatula, press the potatoes firmly into a flat disk. Cook until browned, about 15 minutes. Off heat, invert the rosti onto a plate. Return the skillet to medium, add the remaining 1 tbsp. oil and slide the rosti back into the skillet to cook the other side. Cook, pressing often, until browned, about 15 minutes.
Meanwhile, transfer the meat to a plate. Strain the sauce into a bowl; discard the solids. Pour the sauce back into the pot, add the pearl onions and bring to a boil over medium-high. Cook until the sauce thickens, about 5 minutes. Return the meat to the pot and spoon sauce over top.
Cut the rosti into 6 wedges; divide between plates. Top with the pearl onions, meat, sauce and parsley.