How to Make It
In a large skillet, fry the sausage over moderately high heat, tossing, until lightly browned on both sides. Drain on paper towels. Add half of the beef and pork to the skillet and cook until browned all over, about 4 minutes per side. Transfer to a plate and repeat with the remaining meat.
Heat the bacon fat in a large enameled cast-iron casserole. Add the onions and cook over moderate heat until softened, about 12 minutes. Sprinkle the paprika over the onions and cook, stirring, for 5 minutes. Stir in the beef and pork, sauerkraut, stock, bay leaves and thyme. Add more stock, if necessary, to just cover the meat and sauerkraut.
Bring the stew to a boil. Cover and simmer over low heat for 1 hour. Add the sausage and continue cooking until the beef and pork are very tender, about 1 hour longer. Season with salt and pepper. Let cool, then cover and refrigerate overnight.
Reheat the goulash over moderate heat until piping hot. Discard the bay leaves. Stir in the 1 cup of sour cream and cook until warmed through. Sprinkle with chives and serve with sour cream on the side.