4 tsp. kosher salt
1 Tbsp. (packed) light brown sugar
2 tsp. ground ancho chiles
1 tsp. paprika
1 tsp. ground cumin
1 tsp. granulated garlic
1 tsp. freshly ground black pepper
1 5 to 5 1/2 -lb. flat-cut brisket with 1/4 to 1/2 -inch layer of fat on one side
Store-bought barbecue sauce
4 cups hickory or oak wood chips, soaked in water for 1 hour
Foil broiler pan (for wood chips if using gas grill)
2 foil baking pans (for brisket)
Mix first 7 ingredients in a small bowl. Rub spice blend over brisket. Wrap brisket in plastic; refrigerate for at least 2 hours and up to 24 hours. Bring to room temperature before grilling.
Prepare grill for smoking. If using a charcoal grill: Build a low fire in a charcoal grill (you’ll need to light more charcoal in chimney to replenish two or three times during grilling). Drain 2 cups wood chips; scatter directly over coals. Return top grate to grill. If using a gas grill: Heat grill to medium-low. Drain 2 cups wood chips. Place wood chips in foil broiler pan and place pan directly on gas flame. Return top grate to grill.
Unwrap brisket and arrange fat side up in foil baking pan; place pan on grate over unlit part of grill. Cover grill. Insert instant-read thermometer in top vent. Heat grill to 300°F. Cook brisket, adjusting vents and adding more charcoal or adjusting gas levels as needed to maintain temperature inside grill at 250°F, until an instant-read thermometer inserted into the center registers 160°F, about 3 1 ? 2 hours. Baste brisket occasionally with pan juices and add more drained wood chips as needed.
Remove pan with brisket. Wrap brisket tightly in 2 wide sheets of heavy-duty foil. Discard pan and juices. Place in clean foil baking pan. Return to grill over unlit side, maintaining internal grill temperature at 250°F, until an instant-read thermometer inserted into thickest part of center of brisket registers 190°F, about 1 1\2 hours longer. Transfer brisket in pan to a rimmed baking sheet. Let rest for at least 1 hour and up to 2 hours.
Carefully unwrap brisket, saving any juices in foil. Transfer juices to a small pitcher. Place brisket on a work surface. Thinly slice brisket against the grain; transfer to a platter. Brush brisket with some juices. Serve with any remaining juices and BBQ sauce.