Place the brisket in a saucepan and cover with water. Add bay leaves and salt and boil, uncovered, 5 minutes. Cover and reduce heat to a simmer and cook 2 hours. Remove the meat, let cool slightly and shred with 2 forks.
Place the tomatoes and chillies in a blender and puree until smooth. Strain through a colander.
Heat the oil in a large saucepan. Add onions and garlic and cook until onion is soft, about 10 minutes. Pour in the tomato puree, bring to a simmer and cook until thickened. Stir in the shredded meat, season with salt and pepper, and simmer until as thick as you like it.