Fit a wire rack in a sheet tray. Liberally sprinkle the pork shoulder with salt and pepper, then place on the sheet tray and refrigerate, uncovered, 8 hours or up to overnight.
Heat a large Dutch oven over medium-high heat. Add the sausage to the pan and brown the links on both sides, about 5 minutes per side. Remove the sausage to a plate. Fry the sprigs of rosemary in the fat, flipping frequently, until fragrant, about 1 minute. Remove to the plate with the sausage.
If the pork shoulder is wet, dry thoroughly with paper towels. Add the pork to the Dutch oven and brown on all sides until deeply browned, about 5 minutes per side. Remove the pork to a large plate or baking dish.
Add the cabbage and onions to the Dutch oven and sprinkle with salt and pepper. Cook over medium heat until the vegetables have softened slightly, about 5 minutes. Add the potatoes, wine, mustard and caraway seeds and cook until the wine has almost evaporated, another 8 minutes. Return the pork, sausages and fried rosemary sprigs to the Dutch oven, then add the stock and bring to a simmer. Cover and reduce the heat to low. Let braise until the pork is very tender, about 3 hours.
For a thicker, richer sauce, strain the liquid from the Dutch oven and reduce over medium heat in a small saucepan until it reaches a thin gravy consistency, 7 to 10 minutes. Season the sauce to taste with white wine vinegar, salt and pepper.
To prepare the horseradish sauce, mix together the sour cream and prepared horseradish (add horseradish a tablespoon at a time to taste if you want a milder sauce). Season with salt and pepper.
Remove the pork and sausages to a large serving dish. Shred the pork using two forks. Pour the sauce over the top and garnish with fresh parsley. Serve with sour cream horseradish sauce alongside.
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