Rough chop the vegetables. Set aside.
Spray a sheet pan with pan spray. Drain the corned beef of extra liquid. Spread a thin layer of Dijon mustard on the top of the corned beef. Top this with the barbecue spice. Let it marinate for about an hour so the flavors sink in.
preheat the oven to 450.
Put the beef in the oven at 450 for 15 minutes. Then, cut the temperature back to 275. Roast for an hour uncovered to get some color on it. Then, Spray a sheet of aluminum with pan spray and cover the meat. Cook for another hour and a half to 2 hours. Then, remove the foil. Place the vegetables in the pan alongside and/or under the beef, and, cook another half hour. Add The beer. Cook for about another 20 minutes until the beer starts to soak up the flavor on the pan and dissipate..
The beef should be done at this point. Check to make sure it is tender. It should almost pull apart. Take it out of the pan; and, allow it to rest about 10 to 15 minutes. Transfer the liquid and vegetables to a pot. Add water to the roasting pan and scrape the bottom to release all that flavor (this is known as de-glazing the pan). You may need to repeat this step to get all the flavor up. Transfer this to the pot. Bring the liquid to a boil. Reduce the liquid by about 1/4 to intensify the flavor. Check the flavor. If too salty, add more water or beef broth.
Slice the beef, against the grain into thin slices. Serve hot with the Jus poured over the top.
