Preheat your smoker to 275 degrees.
Place a water pan as close as possible to the heat source of your smoker and fill with water.
Trim your brisket of all excess fat, leaving a 1/4" coverage across the top "fat cap" of brisket. Remove excess fat from deckel area. Trim excess chunks of fat and silver skin from bottom side.
Rub the brisket all over with the yellow mustard.
Mix the kosher salt and black pepper and coat your brisket in an even, liberal coating. If more seasoning is needed, mix the kosher salt and black pepper in a 1:1 ratio, by volume.
Place the brisket on the smoker in the best location on your smoker, avoiding laying it directly over the heat source, if possible.
Roughly every 30 minutes, spray your brisket with the apple cider vinegar mixed with equal parts water.
Let the brisket cook until the internal temperature reaches 155-165 degrees, or until the internal temperature slows or stops rising.
Wrap the brisket tightly in un-waxed butcher paper.
Continue cooking the brisket until an internal temperature of 195-200 degrees is achieved, or a probe or fork easily pieces the meat when poked.
Once proper cooking doneness is achieved, remove from smoker and place in an empty cooler to rest and allow the internal temperature to slowly lower to a manageable temperature. Between 1-3 hours of rest time is recommended.
After proper rest period is achieved, unwrap and drain off any excess drippings and save for future use.
Slice the meat against the grain, changing directions as the point and flat muscles begin to overlap.