Instant Pot Fettuccine Alfredo with chicken, or without, is a dump it all in and push start type of recipe.
Place the butter and garlic in the pot.
Pour in the chicken broth and 1 cup of the heavy cream.
Sprinkle in the fettuccine noodles, in a random pattern, and gently press them down.
If Adding Chicken: Add the chicken, and space evenly over the noodles. Sprinkle with the salt and pepper.
Press down on the mixture to submerge as many of the noodle as possible. Then place the lid on the pot, lock in place, and set the steam release knob to Sealing position.
Press the Pressure Cook/Manual button or dial, then the +/- to select 6 minutes (7 minutes for a softer noodle). After the cook cycle has finished, let the pot sit undisturbed for 5 minutes (5 minute natural release).
Manually release the remaining pressure in short bursts so no sauce spews out with the steam. When the pin in the lid drops, Carefully open the lid.
Remove the chicken and give the pasta mixture a good stir. It may be a little soupy, but it will thicken up.
Shred the chicken and add back into the pot.
Add the grated parmesan and stir it in. If it's still a little too thin, just add a little more parmesan. If too thick, add the reserved heavy cream.
Place the lid back on, vented, and let the pasta sit for a few minutes to thicken up.
Serve with some nice bread and a salad.