Preheat the oven to 325℉. Rinse the corned beef brisket and add it to a large, oven safe pot with a lid, like a dutch oven. Add the water, and ensure there is enough water to cover the brisket with at least 2-3 inches above it. Quarter the onions and stick the cloves into the onion chunks. Add the onions and all spices to the pot with the corned beef. You can use a bouquet garni bag if you don't want the spices free floating around, but you don't need one.
Bring the pot to boil on the stove. Then turn off the heat and cover the pot. Put the pot into the oven and allow it to cook for 4 hours.
Peel the carrots and potatoes if you'd like, then chop them into large pieces. Add them to the pot in the oven at the 2-hour mark.
After the 4 hours, ensure the carrots and potatoes are cooked through and tender by poking them with a fork. Then remove the corned beef and place it on a baking sheet.
Turn the oven heat up to 400℉, and brown the corned beef for 5-10 minutes until it's darkened and crispy on the top. Then remove it from the oven and allow it to rest for 15 minutes before cutting it. Lift the vegetables out of the broth and arrange them around the corned beef for serving.