In pot large enough to hold brisket, combine 1 gallon/4 liters of water with kosher salt, sugar, sodium nitrite (if using), garlic and 2 tablespoons pickling spice. Bring to a simmer, stirring until salt and sugar are dissolved. Remove from heat and let cool to room temperature, then refrigerate until chilled.
Place brisket in brine, weighted with a plate to keep it submerged; cover. Refrigerate for 2 days if it's thin, a third day if it's thick.
Remove brisket from brine and rinse thoroughly. Refrigerate it for another day uncovered (this is best, to let cure equalize, but if you can't wait, that's ok too).
Combine the pepper and coriander and coat the brisket with it. Smoke and cook the brisket, till tender, as described above. This will keep for a week in the refrigerator. Steam it to reheat or reheat covered in a microwave (gently). Slice thinly to serve.