Preheat the oven (or a covered grill) to 325°F.

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.  (Alternately, if sauerkraut is not excessively salty, use as is. If using fresh cabbage, you can skip this step.) Press to release most of the excess liquid and set aside.  In a large non-reactive skillet, melt 3 tablespoons of the butter over medium-low heat and add the bacon.  Cook for 5 minutes, not allowing the bacon to brown.  Add the onions and continue to cook until they are soft but not browned, 8 to10 minutes.  Transfer bacon-onion mixture to a 4-quart non-reactive ovenproof Dutch oven. (If using fresh cabbage, add it to the drippings remaining in the skillet and cook, stirring occasionally, until slightly wilted, 4 to 6 minutes.)

Add the drained sauerkraut (and/or cabbage) to the Dutch oven 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 Dutch oven.  Add the ham hocks, chicken stock and beer and stir to combine.  Add the new potatoes to the pot, cover and bake for 2 hours, undisturbed.

In a large sauté pan over medium heat, brown the sausages on all sides and set aside.

When the cabbage and hocks have baked for 2 hours and the hocks are tender, remove the casserole from the oven.  Place the sausages on top of the cabbage. If the liquid has evaporated to below two-thirds full level, add a bit more water to the casserole at this time.  Cover the casserole and return it to the oven.  Cook for about 30 minutes, or until the sausages are cooked through.  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, potatoes and cabbage.  Pass the mustard at the table.