After soaking, boil the beef bones for about 5–10 minutes with 1 teaspoon salt and 1 teaspoon vinegar to remove impurities. Rinse the bones thoroughly under running water.

Add the roasted spices, onion, and ginger to a large pot with the cleaned bones. Cover with 5–6 quarts of water (about 5–6 liters) and simmer over medium heat for several hours. As the broth reduces, add more water to maintain the original level. Season with fish sauce, salt, and rock sugar to taste.

Cook the dried pho noodles in boiling water for 8–10 minutes, then rinse with cold water and briefly dip in hot water to prevent sticking. Quickly blanch the bean sprouts and rare beef. Thinly slice the remaining white onions and soak in ice water to reduce sharpness. Chop the green onions. To serve, add bean sprouts, noodles, green onions, sliced onion, and beef to a bowl. Ladle hot beef broth over the top and enjoy with lime, chili, hoisin sauce, and hot sauce.