Turn IP on to sauté.
Add cinnamon stick, star anise, and cloves to dry pot. Sauté 1-2 min until aromatic.
Add ginger and onion, cook in dry pot 1 min until aromatic.
Add water to a depth of 2 inches.
Add marrow bones, beef tendon, apple, and salt. Add water to "max fill" line of your IP.
Pressure cook on high pressure manual setting for 1 hour 15 min. Allow pressure to release naturally for 20 min.
Strain stock through fine mesh strainer. Stock may be cooled and refrigerated at this point for use later, or you may proceed with the recipe. Transfer tendon to cutting board.
Transfer strained stock either to pot on stovetop or back into IP on sauté. Heat to simmer/low boil. Add rock sugar and fish sauce to taste. Salt may be added as well. Keep in mind that this stock will flavor the rest of the ingredients, so it should be strongly flavorful.
While stock simmers, thinly slice beef tendon with an extremely sharp knife, to a thickness of no more than 1/4". Return to simmering stock.
Follow package directions for rice noodles. Many require a very brief boil. Do not overcook.
Assemble 4 bowls: Divide rice noodles equally. Top noodles with thinly sliced steak, spreading individual pieces in a single layer over the noodles (overlapping is fine). Pour piping hot broth into the bowls, making sure to include the sliced tendon, and serve.
Offer garnish plate consisting of bean sprouts, fresh herbs (basil, mint, cilantro), and thinly sliced chiles. Diners should add these directly to soup. Offer hoisin sauce and sate/sriracha as well, and provide small dishes so diners may dip meat separately into sauce if they choose. Slurp away!