Sprinkle the brisket on both sides with the cayenne, 1 1/2 teaspoons seasoning salt and 1/2 teaspoon black pepper; set aside.
Place a stockpot or Dutch oven over high heat and coat with the grapeseed oil. Add the minced garlic and then the brisket, fat-side down; cook until evenly browned, 5 minutes. Flip the meat and brown the reverse side for 5 minutes. Add the stock, carrots, celery, onions and garlic cloves. Cover, turn the heat down to very low and cook for 2 hours.