Heat the oil in a large pot until nearly smoking. Add the meat and cook until nice and brown on all sides, adjusting the temperature to agressively brown the meat, not burn it, 7 to 10 minutes. The meat will stick to your pot at first, but will release when browned.

Add the green onions, garlic, ginger, chile-garlic paste, cinnamon sticks and aniseed and stir until fragrant, 15 to 20 seconds.

Pour in the beef broth and soy sauce and bring to a boil. Reduce the heat to a low simmer and partially cover the pot. Cook the meat until it is very tender and almost falling apart. 1 1/2 to 2 1/2 hours. Add the cornstarch and water mixture and simmer briefly until thickened. Add the spinach and simmer until wilted. Serve the meat, spinach and sauce over rice or noodles in deep bowls.