01 -
Coat the brisket evenly with yellow mustard and barbecue rub, then refrigerate for 1 to 2 hours to allow flavors to develop.
02 -
Preheat smoker to 210°F. Smoke brisket over hickory pellets for 9 to 10 hours. Wrap brisket in butcher paper and return to smoke until fork-tender, then allow to rest before slicing.
03 -
Dice onions and sauté in a skillet over medium heat until soft and golden brown, about 15 to 20 minutes.
04 -
Layer sliced brisket, Colby Jack cheese, Provolone cheese, fried onions, caramelized onions, and barbecue sauce evenly between sourdough bread slices.
05 -
Heat a cast iron skillet over medium heat. Toast each sandwich until the bread is golden brown and the cheese is fully melted, about 4 minutes per side.
06 -
Slice sandwiches in half and serve hot.