Combine pepper and salt in a small bowl. Rub 2/3rds of the salt/pepper mix over surface of brisket. Reserve remaining one-third of mixture.
Place brisket in a vacuum seal bag, if you need to cut it in 1/2 and place in two bags. We managed to stuff ours in one large bag. Seal bags with vacuum sealer and place in fridge for 2 hours to rest.
Set your precision cooker to 135°F (57°C) for brisket with a tender, steak-like texture that you'll be able to slice, or 155°F (68°C) for shredded type brisket
Add brisket to a large water bath ( we used a plastic storage container) and cover container with either aluminum foil, lid, or weight the brisket down with something heavy like a wire rack or stainless steel steamer baskets. See post for more info.
Cook for 24 to 36 hours at 155°F or 36 to 72 hours at 135°F. I know it sounds like a lot, but you basically ignore it on the kitchen counter till its ready! Totally hands off.
Allow cooked brisket to cool to room temperature before proceeding (you can place it in an ice cold water bath to speed the process up) Brisket at this point can be stored in the refrigerator at this stage for 5-7 days before finishing.
Adjust oven rack to lower-middle position and preheat oven to 150 C (300F), or you can use your ovens convection setting and heat to 135°C/ 275°F instead.)
Remove brisket from bag and blot dry with paper towels. Reserve some of the liquid from the bag to make amped up barbeque sauce if desired (See post for details)
Rub the remaining salt-and-pepper mixture into surface of brisket. Place brisket on a wire rack set in a rimmed baking sheet, fatty side up, and place in oven. Roast until a deep, dark exterior has formed, about 1.5-2 hours.
Transfer brisket to a cutting board and cover loosely with foil. Allow to rest until the temperature drops to between 63 and 74°C (145 and 165°F ), about 30 minutes. Slice against the grain into thin strips and serve with bread rolls, dill pickles, and sliced onion, and any other condiments you like.