1. Rinse the corned beef.
2. Add it to a large dutch oven fat side up. Enameled cast iron, like Le Crueset, works very well here.
3. Cover it with water by about 1 inch.
4. Bring it just to a boil, reduce the heat, cover it partially and let it cook for 15 minutes.
5. After 15 minutes, skim the foam off the top of the water.
6. Add the spices to the Pot. I use a tea strainer to keep the seeds from getting all mixed up with everything. You can also just wrap them in a piece of cheesecloth or just toss them into the water not wrapped at all. They certainly won't hurt anything.
7. Bring the water to a simmer, cover the pot and cook the corned beef for about 2 1/2 hours, checking the pot occasionally to make sure it is just at a low boil.
8. About 10 minutes before the corned beef is done, if I am using whole onions I will put them in the pot with the corned beef for those last 10 minutes. Also at this time, preheat the oven to 200° F.
9. Remove the corned beef and put it in a 9" x 13" casserole dish and cover with foil. Place it in the preheated oven while the vegetables are cooking. At this point, if you are going to be saving some of the corned beef for later, you can cut that piece off and put it on a plate and cover it loosely with foil until it cools. Then wrap it in foil and store it in the refrigerator for 3-4 days or in the freezer for several months.
10. Depending on how you like your vegetables, you can use small or large pieces and adjust your cooking time accordingly. I like to use smaller potatoes and leave them whole but if they are larger I will cut them in half. For carrots and turnips I cut them in 1" pieces. For onions I like to leave them whole and add them about 10 minutes before the potatoes and carrots. For the cabbage I like to quarter it and cook it that way and then before serving either cut it in chucks or just pull the leaves apart so everyone can get a little or a lot.
11. After removing the corned beef, add the potatoes, onions, carrots and root vegetables to the liquid and cook for 10 minutes. The onion has already been in the broth cooking for about 10 minutes at this point.
12. Cut the cabbage into wedges and remove the solid core. Add it to the pot and continue cooking for another 10-15 minutes until the vegetables are cooked to your liking. I tend to prefer some bite to the vegetables rather than having them be too soft but everyone has their preferences. And there will be long discussions (over beer of course) as to whether the cabbage should be lightly cooked so it still has a little crunch to it or cooked until it melts in your mouth like butter.
13. Remove the vegetables to a sheet pan or other wide platter to let them cool a little bit and stop the cooking process.
14. Remove the meat from the oven and slice it across in thin slices and arrange the slices on a platter. Place the vegetables around the meat and serve.