Place your brisket, fat-cap side up, on a large cutting board. Brisket has a fat layer covering the meaty part, and the fat layer can vary in thickness. If trimming the brisket, make sure to leave a narrow layer of fat (about ¼-inch thick) on the outside of the brisket to protect the beef from drying out.
Most of it is a hard fat that doesn't render, preventing the meat from absorbing the smoke flavor. There's a fairly thick vein of fat between the point and flat. Don't trim this part, as it keeps the brisket moist. You can remove this part as you slice the brisket.
In a small bowl, stir the brown sugar, salt, paprika, ground pepper, mustard, oregano, cumin, garlic powder, and onion powder.
Rub the brisket with yellow mustard and Worcestershire sauce or water. This makes the spices stick to the brisket, but don't worry because you won't taste the mustard.
Season the brisket with dry spice mix evenly over all sides of the brisket. Reserve the rest for the burnt ends.
Preheat your pellet grill to 225-250°F (107-121℃). Follow the manufacturer's instructions for your specific grill, and use your choice of wood pellets (I used a blend for this recipe).
Place the brisket in the pellet grill, fat-side up, and smoke for approximately 6 hours, or until the internal temperature of the brisket is between 165-170℉ (74-77℃) and your brisket has developed a good bark (flavorful crust that forms on the brisket's surface).
Take the brisket from the smoker and tightly wrap it with butcher paper or foil. (Foil cooks it faster and tenderer but may ruin the bark, while butcher paper can preserve its texture but may take longer to cook.)
Place the wrapped brisket back in the pellet grill and continue smoking until the internal temperature is between 203-205°F (95℃).
Place the wrapped brisket in a cooler or a warm, dry place and let it rest for at least 30 minutes.