Put the beef shank, ox tail, and beef chuck in a large pot with enough water to cover the meat. Bring to a boil. Once the water boils, take the meat out and set aside. Pour out all the water and put the meat back into the pot. (Throwing away the water gets rid of most of the impurities and any gross flavors from the meat.) Add fresh water to the soup pot until it just covers the meat. Be careful not to add too much water as it will make the soup weak in flavor.
While the water is boiling in the step above, place the onion and ginger in the oven for 20 minutes on broil. Set aside.
Next, saute the coriander seeds, fennel seeds, cardamom seeds, star anise, and cinnamon stick for 1-3 minutes until you smell a toasty aroma. Add all the spices to a piece of cheese cloth. Tie the corners together to create a spice pouch. Set aside.
Bring the water in the soup pot to a boil. Scoop away any impurities you see. Simmer for an hour. Continue to check on the soup every 15 minutes and scoop away any impurities you see. This will ensure that your soup appears clean.
Once the soup has simmered for an hour, take out the beef chuck and slice into thin pieces and set aside. Simmer for another hour and then take out the ox tail and beef shank. Remove the meat from the bones. Thinly slice the meat and set aside. Put the bones back into the soup pot.
Simmer for an hour more. The soup should be done after this time period. Take the spice pouch out of the soup and throw away.
Cooking the noodles: Boil water and add in the pho noodles. Let it simmer for about 2 minutes or until noodles are done. If you are using fresh noodles, submerge noodles in boiling water for 5-10 seconds and they're done!
Put some noodles in a soup bowl. Add fish sauce, bean sprouts, cilantro, and green onions on top. Top it off with some of the beef chuck, beef shank, and ox tail meat you set aside earlier. Finally, ladle enough soup into the bowl so that it covers the noodles and toppings to your liking.
Optional: Season with hoison sauce and sriracha to your liking.
The longer you simmer your broth, the more flavor it will have. I like to make the broth a day before I want to eat it.