Place the sauerkraut in a colander and rinse briefly to remove some of the salt from the brine-don't rinse it too much, or you will lose a lot of the flavor. (Alternatively, if the sauerkraut is not excessively salty, use as is.) Press to release most of the excess liquid and set aside. In a large nonreactive skillet, melt 3 tablespoons of the butter over medium-low heat and add the bacon. Cook until most of the fat is rendered, about 4 minutes. Add the onions and continue to cook until they are soft but not browned, 8 to 10 minutes. Transfer the bacon-onion mixture to a nonreactive roasting pan or large ovenproof Dutch oven. Add the drained sauerkraut and toss to combine. Using a small piece of cheesecloth, make a bouquet garni with the thyme, bay leaves, peppercorns, juniper berries, and garlic and place in the baking dish. Add the ham hocks, chicken stock, and beer and stir to combine. Cover the casserole and bake, undisturbed, until ham hocks are mostly tender, about 1 1/2 hours.
Meanwhile, melt the remaining tablespoon of butter in a large skillet over high heat and brown the sausages on both sides. Set aside. Brown the pork chops and set aside.
When the hocks are mostly tender, remove the casserole from the oven. Place the sausages on top of the sauerkraut. If the liquid has reduced to less than 2/3, add a bit more water. Cover the casserole and return it to the oven. Cook for about 30 minutes, or until the sausages are tender and heated through. Add the pork chops and press them into the sauerkraut. Cover and return to the oven and cook until pork chops are heated through and tender, about 30 minutes longer. Remove the casserole from the oven and discard the bouquet garni. Serve immediately, with each person receiving some of each of the sausages, part of a hock, part of a pork chop and some of the sauerkraut. Pass the mustard at the table.