Slow Roasted Corned Beef and Cabbage

in the bottom of a large casserole dish, I put some onions, potatoes, celery and carrots.  Sprinkled with pepper.  Put the three lb corned beef brisket on top and sprinkled the seasoning packet on top of it.   Put maybe 3/4 cup of water into the bottom of the pan.  Covered with foil and into the oven at 9:30 a.m.  When I got home at 2:30, I put about 1/3 or 1/2 of a cabbage (cut up) on top of it all and put it back in the oven.  When I tested the meat at three p.m. I realized that the meat and vegetables were well done.  So I removed them from the pan and left the juice and cabbage in the pan, into the oven at 300 degrees for about a half hour or so.  I made a glaze of mustard and brown sugar and turned the brisket over and spread the glaze on top.  Put the meat and vegetables back into the oven for ten minutes covered (to reheat), then five minutes with the foil off.  By that time the cabbage was crisp/tender.   Delicious!