Toast the mustard seeds, black peppercorns, and coriander seeds. Place these spices along with all the other ingredients, except the brisket, in a large stock pot. Bring to a boil. Remove from heat and let cool at room temperature. Place the brisket in the stock pot and place the stock post into your refrigerator. Let sit for 2-3 days.
Remove the brisket from brine. Thoroughly rinse it of in cold water and pat dry. Toast all of the spices and then place them in a spice grinder. Grind until they reach a coarse ground. Firmly press the spice rub firmly into the brisket, being sure to cover the entire surface. Place the brisket on a wire rack that’s been placed on a metal sheet. Refrigerate until ready to smoke.
Place your brisket in a smoker. Set your smoker to 225 degrees, and place your preferred water-soaked wood chips inside. Depending on the thickness of the brisket, cooking can take 10-12 hours. The brisket is ready when the internal temperature hits 180 degrees Fahrenheit. Throughout the smoking process, replace the wood chips to retain an even smoking.
When the smoking is complete, remove the brisket from the smoker and let it cool for at least 30 minutes before you slice it.