If you choose to soak your noodles, begin doing so now by submerging them in very warm water. You can also boil your noodles and drain just before eating.
Peel and quarter a whole onion. Do your best to keep the quarters attached and not peeling apart.
Peel the piece of ginger using a spoon, cutting off any hard to reach knobs. Roughly slice the ginger into thick pieces.
If using whole shiitakes, remove the stems and slice the caps longways.
Turn your Instant Pot on to 'sauté'. Once hot, add a small amount of neutral oil, then sear the onion quarters.
Once the onion pieces are beginning to crisp, throw in the ginger slices and toss.
Next, add all of the whole spices and stir to combine. The onion pieces may break apart and that is okay.
Add the sliced mushrooms and cook for 2-3 more minutes.
Next, add the water and broth to the pot.
Stir to combine, then close the lid, set the valve to sealing, and pressure cook on HIGH for 15 minutes.
When the 15 minutes are up, perform a natural pressure release (meaning simply press cancel and do nothing) for 10 minutes. After the 10 minutes, release remaining steam.
If you haven't been soaking your rice noodles already, just give them quick boil now, then rinse with cool water after draining.
Open the lid on the Instant Pot.
Use oven mitts or towels to remove the inner pot. Place a large bowl in the sink, with a fine-mesh strainer over the bowl.
Carefully pour the contents of the Instant Pot into the strainer, then lift the strainer out of the bowl. You should be left with a warm-brown broth in a bowl.
Place cooked rice noodles into serving bowls. Ladle broth over the noodles.
Garnish the bowls with limes, basil, cilantro, some of the cooked shiitakes, chili oil, or more!
Serve hot and enjoy.