Trim the fat on the brisket, leaving about ¼ inch.
Apply a layer of mustard as a binder.
Generously coat the brisket with the barbecue spice rub.
Place the brisket in a 225°F oven and cook for about 8.5 hours until it reaches an internal temperature of 180°F.
Wrap the brisket tightly in foil and return it to the oven, continuing to cook until it reaches an internal temperature of over 200°F.
Let the brisket rest, wrapped in a towel, for 1-1.5 hours.
Slice the brisket and serve on a toasted and buttered roll with jalapeño mayonnaise, barbecue sauce, and bread and butter pickles.
