Start by charring your ginger and onions. Use tongs to hold the ginger and onions over an open flame, or place directly on an electric burner. Turn until they’re lightly blackened and fragrant about 3 minutes. Rinse away the blackened skins and set aside.
Place the bones and beef chuck in large stockpot and add water to cover. Bring to a boil and boil for 5 minutes. Drain in a colander and rinse. This process will give you a much cleaner broth.
Set aside your beef chuck in the refrigerator for use later. Transfer the bones to your Instant Pot, along with the charred/cleaned ginger and onions. Add the scallions, fish sauce, sugar, and salt.
Now toast the spices (star anise, cloves, cinnamon stick, black cardamom, fennel seeds, and coriander seeds) in a dry pan over medium low heat for about 3 minutes, until fragrant. Use kitchen string to tie up the spices in a piece of cheesecloth, and add it to the pot. Cover everything with 3 ½ quarts of water.
Seal the Instant Pot and place on the manual high pressure setting for 120 minutes. Allow the pressure to release naturally (15-30 minutes). Add the beef chuck and put back on the meat/stew setting for 30 minutes.
Use the Quick Pressure Release, and when the Instant Pot is once again safe to open, skim the broth for excess fat and impurities. Adjust seasoning by adding more salt, sugar, and/or fish sauce to taste.
To serve, boil the noodles according to package instructions. Add to a bowl. Place some slices/shreds of the beef chuck on the noodles. Cover with broth, and garnish with sliced onion, bean sprouts, and Thai basil, and be sure to squeeze some fresh lime juice over the top! You can also add some cooked beef balls or thinly sliced eye round if you like.