Place onion garlic, mushrooms, butter, mustard, soy sauce, salt, pepper and water into the Instant Pot and stir.
Add in pasta and stir.
Close the lid and press PRESSURE COOK. Cook on HIGH for 5 minutes and then let the pot rest undisturbed for 5 minutes. Then, release all remaining pressure.
Open the lid, stir in sour cream and parsley and serve.