Step 1: Rinse off the brisket under cold running water and drain. Trim the fat so a 1/4- to 1/2-inch thick layer remains.
Step 2: Make the brine: Place 2 quarts of water, the salt, and pink salt in a stockpot and bring to a boil over medium-high heat; whisk until the salt crystals are dissolved. Stir in the onion and garlic. Stir in the cold water and let cool to room temperature. Place the brisket in a large resealable plastic bag. Add the brine and seal the top. Place in a second bag and seal, then place in a baking dish or foil pan to contain any leaks.
Step 3: Brine the brisket for 5 days in the refrigerator, turning it once a day. Remove the meat and discard the brine. Make a new batch of brine as per the directions above. When the brine has cooled, re-bag the meat and the brine. (This is called “overhauling.”) Let the brisket brine for an additional 5 days, turning once a day as before.
Step 4: Meanwhile, the last day, make the rub: Place the peppercorns, coriander seeds, mustard seeds, brown sugar, and ginger in a food processor and grind to a coarse powder, running the machine in short bursts. The final rub should feel gritty, like coarse sand.
Step 5: Drain the brisket, rinse under cold water, and blot dry with paper towels. (Discard the brine.) Place it in a roasting pan and thickly crust it on both sides with the spice rub.
Step 6: Set up your smoker according to the manufacturer’s instructions and preheat to 225 degrees. Add the wood as specified by the manufacturer.
Step 7: Place the pastrami fat side up in the smoker. Smoke the brisket until crusty and black on the outside and cooked to about 175 degrees inside, 8 hours.
Step 8: Wrap the pastrami in non-plastic lined butcher paper. Continue smoking until the internal temperature is 195 degrees and the meat is tender enough to pierce with a gloved finger or wooden spoon handle, 2 to 4 hours more.
Step 9: Transfer the wrapped pastrami to an insulated cooler and let rest for at least 1 hour. Slice crosswise for serving. You don’t really need a sauce or condiment, but I wouldn’t say no to some horseradish mustard.