1) Make the dry rub by mixing together all the ingredients in a bowl. Preheat oven to 350 degrees. Trim off some fat from the brisket.
2) Take spice rub and cover brisket with it on both sides.
3) In a large heavy roasting pan, heat a few Tablespoons of oil. When it is really hot, put the brisket in and sear it well on both sides. This should take about 5 minutes per side.
4) Once you pull the brisket out, add 2 Cups of chicken stock to the pan. Use a spatula to stir up any little burned bits stuck to the pan.
5) Once chicken stock is simmering, add prunes, brown sugar, bay leaf, and Porter. Bring that mixture to a boil.
6) Set brisket in this liquid, fat side up. Then layer all those sliced onions on top of the brisket with the garlic cloves! Cook this, covered, for one hour.
7) Take it out and you should see that the onions have turned translucent.
8) Turn the brisket over and push all of the onions into the braising liquid. Cook this uncovered for 30 minutes.
9) Add another cup of chicken broth, cover it and cook it for another 90 minutes.
10) Meanwhile, prepare mushrooms and carrots. You want pretty large pieces or they will just disintegrate.
11) After the 90 minutes, take the brisket out and add the other veggies and one more cup of chicken broth. Set the brisket back on top of the veggies so the veggies are mostly submerged in the braising liquid. Cook this for another 45 minutes with the lid on.
12) Let it cool at room temperature for at least 30 minutes, then let it sit in the fridge for at least 24 – 48 hours.
13) 24 – 48 hours later, get a spoon and gentle spoon off as much fat as you can. Don’t worry about getting all of it.
14) Lift the brisket out of the pot and put the pot with the sauce and veggies over high heat. You want it simmering nicely!
15) Slice the brisket against the grain. Lay out all the slices in a large baking dish.
16) Once the sauce and veggies has come to a simmer, very carefully pour it over the cold brisket slices. Cover this with foil and bake it for yet another 75 minutes at 350 degrees.
17) Finally. Once that baking is done, you can eat it up! Serve up a few slices with all the veggies and sauce.