Rub Brisket all over with dry rub. Place in a glass dish and cover with clingfilm. Marinate for at least 2 hours preferably overnight. Bring to room temperature when ready to cook.
Preheat oven to 170°C. Place roasting pan over a cooktop, and bring to a medium‐high heat. Add 1 tablespoon oil and then the brisket. Brown all over and then add the rest of the oil onions and garlic to the pan. Allow the vegetables to soften, about 8 minutes. Add stock, scraping bottom of pan. Cover tightly with foil and place in oven. Cook for 2 hours and 45 minutes.
Turn the oven to grill at 200 degrees and uncover brisket. Cook for 15 minutes turning once halfway through. Remove once crisp, set aside.
While meat is resting, turn oven onto 200 degrees, place potato slices on a baking sheet lined with baking paper, toss in sea salt and remaining oil and roast for 10-12 minutes until crisp.
Serve meat shredded and chopped in warm buns with pickles, onion and crisp sweet potato chips.
You can serve with store bought sweet potato chips.
You can marinate beef for up to 48 hours to get a much richer flavour.
You can pickle the onions quickly by squeezing lemon juice over them before serving if the flavour of raw onion is too strong for you.