Parboil oxtails for 5-10 minutes.
Strain and thoroughly rinse the meat with cold water.
Slice onions in half.
Char onions and ginger in a pan or instant pot (pressure cooker) on saute mode. Remove from the pan.
Add spices to hot pan and roast for 1 minute. Pour spices into a spice bag and tie with a knot.
Place the beef oxtails, tendons, onions, ginger, spice bag, and rock sugar into the instant pot (pressure cooker).
Fill the pot with water just below the max fill line.
Add 1/4 cup of fish sauce to the pot.
Close the lid of your instant pot, place the vent on sealing, set the timer on manual for 50 minutes.
Soak noodles in lukewarm water for 30 minutes.
Bring a pot of water to boil.
Cook noodles for 1-2 minutes or until desired texture is reached.
Remove the noodles from the pot and rinse with cold water.
Add thinly sliced beef (eye of round) to hot water and let cook for about 30 seconds - 1 minute (optional).
Once the timer is complete quick release the pressure
Remove tendons from the pot and slice into thin bite-sized pieces.
Remove the spice bag, ginger, and onions and discard.
Skim fat off the top of broth (optional).
Add additional fish sauce to taste (optional)
Add noodles, broth, tendons, and meat to a bowl.
Add desired toppings.
Enjoy!