Set the Instant Pot to saute, and give it a full 8 minutes to get screaming hot. Add the oil to the pot. Let it heat up for about 10 seconds, then add the onion and the ginger to the pot. Stir to coat in the oil, then let the onion and ginger sit in the hot pot on saute for 2-3 minutes, or until they start to char and blacken.
Flip all the pieces of onion and ginger, and add the star anise, cinnamon stick, cloves, coriander, and fennel seeds to the pot. Toast for 2 minutes, stirring frequently.
Add the water to the pot, making sure to scrape up any lingering burnt pieces of onion and ginger from the bottom. Add the beef bones, fish sauce, and the salt.
Place the lid on the pot and turn it to lock it into place. Move the vent to sealed position. Cancel the saute function and press the Pressure Cook button. Set the timer for an hour and 15 minutes.Once the timer is finished, let the pot sit for another 30 minutes ( Natural Pressure Release for 30 minutes ), then carefully and slowly open the pressure valve to release any remaining pressure.
Prepare the noodles according to package directions.
Strain everything that was in the pot so that all is remaining is the broth.
To serve - place ¼ of the noodles in a large bowl. Top with HOT broth. Add slices of raw beef to the hot broth ( it will cook in the broth! ). Serve with various toppings. I love mine with lime, lots of mung bean sprouts, basil, and sriracha.