This dish is great in the fall and winter, a little too warming for the summer (but that's way they make Barbecue Ribs). For the pork, make sure it is NOT a lean, tender cut. This dish will dry out a pork loin, for instance. Go for shoulder (Boston Butt, or shoulder roast), or country style ribs, or a fresh picnic. I tell you how to make it in either a pressure cooker? or a dutch oven?.
If using a dutch oven, preheat oven to 3250F.
Cut the pork into large pieces, 1/4-1/2 lbs hunks. In the pot you will be using, heat the oil over medium high until it shimmers, then brown the pork on all sides. Do not crowd the pan or it won't brown. Pull out the pork and set aside.
Put the onions, garlic and celery in the pan and cook until the onions are lightly browned.
Meanwhile, drain the sauerkraut and rinse lightly to remove a little of the sourness. Peel and rough chop the apples, and mix the apples, sauerkraut and brown sugar.
Put half the sauerkraut in the pan and mix in with the onions. Layer the pork on top of the sauerkraut. Cover the pork with the remaining sauerkraut. Bury the bay leaf in the sauerkraut.
If using a pressure cooker, bring to pressure and cook for 20 minutes, then take off the heat and release the pressure.
If using a dutch oven, cover and put in the oven for 1 1/2 hours.
Make dumplings. Remove lid from your pot and remove the bay leaf. Spoon the dumplings on top of the sauerkraut and steam, covered, for 20 minutes either on top of the stove or back in the oven, until light and fluffy.
Do not pressure cook the dumplings. While it "sort of" works, odd chemistry takes place. I once made dumplings with buttermilk and then pressure cooked them with this recipe. Something made them turn brown and look like whole wheat dumplings. They tasted OK, but the look was bad. Steaming works just fine.