Heat the oil in a bowl over medium heat until hot. Place the brisket in the bowl. Brown until browned on all sides. Remove the brisket from the bowl and season with salt and pepper, to taste. Add the onion, cumin and garlic to the bowl, cook the mixture, stirring for 3-5 minutes or until the onion is soft and crisp. Return the brisket to the bowl, facing the side of the fat layer upwards. Add the broth and tomato sauce, bring to a boil. Reduce heat to low; cover the pot and simmer the meat for 2 ½ to 3 hours or until tender.
How to prepare crispy tortillas: Divide two tortillas in half, then cut crosswise into slices about ½ cm wide. Spread the slices in a single layer on an ovenproof sheet and spray with nonstick cooking spray. Grill in the oven at 205°C for 4-8 minutes or until crispy. Set aside.
Remove the brisket from the cooking pot. Remove the accumulated fat from the broth. Trim the fat from the brisket piece. Cut the meat into 4-6 pieces and tear with two forks into twine. Place the meat back in the bowl. Add the corn and pepper sauce. Cook for 20-25 minutes, add the chopped coriander. Season with salt and pepper, to taste.
Pour the soup into special dishes. Garnish each dish with tortilla slices, coriander sprigs, avocado slices and cheese, to taste.
