Stir together beef broth, water, onion, garlic, star anise, cloves, ginger, cinnamon stick (and fish sauce, if using) in a large stockpot, and bring to a boil over high heat. Cover, reduce heat to medium-low, and let simmer for at least 20 minutes.
Meanwhile, cook the noodles according to package instructions. (If your package of noodles — like mine — did not have instructions, simply bring a large pot of water to a boil. Then cook the noodles until al dente, about 3 minutes.) Immediately drain the noodles, and rinse with cold water to stop the cooking. Drain and set aside.
When you are ready to serve the soup, fill the serving bowls about halfway full with noodles. Then cover with the hot broth, and immediately stir in the steak so that it cooks. Top with your desired garnishes.
(*Most people stir the cilantro, ginger, lime, jalapenos and Thai basil into the broth to give it extra flavoring, but you don’t necessarily need to actually eat those ingredients whole.)