Rinse the beef bones and place them on a cookie sheet. Air fry or bake at 400°F for 20 minutes until browned.
Transfer the beef bones to a medium-sized pot. Fill with water and boil for 10 minutes to draw out the impurities from the bones.
Drain the bones and rinse off any scum. Transfer the bones to a large stock pot with 6 quarts of water and bring to a boil.
Heat a skillet over medium-high heat and without oil, char the halved onion and ginger slices on both sides. Transfer into the large stock pot.
Turn the heat to down to low for the skillet. Add the SPICES (cinnamon sticks, cardamom pods, star anise, and cloves). Again, do not use any oil. Gradually toast the spices to bring out the flavors. Stir periodically until they become aromatic and darkens in color. Add the coriander last since they're small and brown quickly.
Put the spices in a spice/tea bag or wrap and tie them in a cheesecloth. Add the spice pouch to the stock pot along with fish sauce, salt and sugar.
Bring to a boil then lower the heat to a simmer, cover with the lid slightly ajar. Simmer for 6 hours. Replenish the water as needed.
During the 6 hours, periodically skim any scum or impurities off the surface of the broth.
After 6 hours, remove the spice pouch, ginger slices, and onion halves. Skim off as much fat as you can. To make the broth as clear a possible, use a fine mesh strainer to strain out impurities and any bits you see.
Add more salt and fish sauce to taste. The broth should taste slightly on the salty side. Once the broth is poured over noodles and toppings added, the flavor gets diluted.
Cooking the Noodles
If you're using dried pho rice noodles, be sure to rehydrate ahead of time according to the package instructions.
Bring a pot of water to a boil.
One serving at a time, place a handful of noodles into a fine mesh strainer with a handle or a noodle strainer. Lower it into the boiling water for 5 seconds. Remove the strainer and shake out the excess water. Transfer the noodles to a large soup bowl. Cook the noodles al dente since it'll continue to soften in the broth.
Putting it All Together
To assemble a bowl of Pho Tai, add freshly cooked noodles in a bowl. Top with thinly sliced raw beef, onions, scallions and cilantro.
Ladle hot broth over the beef. Top with fresh bean sprouts, basil, jalapenos, black pepper and a squeeze of lime.
Serve with hoisin sauce and sriracha for dipping the meat as well as a side of broth with a bone.