Trim the brisket, leaving a ¼-⅓ inch layer of fat.
Season the brisket with the rosemary salt and black pepper.
Bake the brisket at 250°F (120°C) until it reaches an internal temperature of around 160°F (71°C).
Wrap the brisket in butcher paper that has been brushed with beef tallow and return it to the oven at 250°F (120°C) until it reaches an internal temperature of 203°F (95°C).
Remove the brisket from the oven and perform doneness tests until it reaches an internal temperature of 160-170°F (71-76°C).
Set the oven to the lowest temperature, around 165°F (74°C), and place the brisket back in the oven for 10-12 hours.
Remove the brisket from the oven and let it cool down to 150°F (65°C) before slicing and serving.