Preheat oven to 300 degrees Fahrenheit.
Remove corned beef from packaging and rinse under water and pat dry until all the curing liquid is removed.
Prepare all the veggies and potatoes by chopping them into large chunks.
Heat a large dutch oven over medium heat on the stove. At least a 7 quart or larger.
Add olive oil and sear the brisket on both sides for about 1-2 minutes each. Place brisket fat side up and sprinkle on the packet of seasoning that it came with.
Pile on all the veggies and potatoes and add beef stock until the brisket is completely submerged. Placing all the veggies on top will help keep the brisket submerged.
Bring to a light simmer over medium heat.
Cover with the lid and carefully transfer to the oven.
Bake until the internal temp of the beef is between 180-205 degrees. It will take about 2.5-3 hours. The beef will be most tender the closer to 205 it gets. But be careful! If it goes over 205, it may start to get really tough. See notes
Remove the dutch oven and transfer the brisket to a plate and cover with foil. It needs to rest for about 20 minutes.
Take the wedges of cabbage and place them in the liquid and return to the oven, uncovered for 20 minutes. Or simmer on the stove until they are tender .
Remove cabbage and veggies from the stock, slice the brisket against the grain, and serve warm. Don't forget your side of soda bread to go with it!