Turn on the Instant Pot Sauté setting. When the pot is hot, add the oil, butter, and diced onion. Cook, stirring occasionally, until the onion is just starting to turn translucent (2–4 minutes).

Add the ground beef and stir, breaking up the meat, leaving a few larger chunks for texture. Cook until the beef is just a little pink — this helps keep the meat tender when pressure cooking.

Add the thyme, salt, pepper, garlic, and Worcestershire sauce. Stir and cook for about 1 minute until fragrant.

Add the sliced mushrooms and mix well. Cook for another minute until they begin to release some juices.

Pour the beef broth and add the beef bouillon while stirring, scraping the bottom of the pot to lift any browned bits.

Add the egg noodles and press them gently into the mixture to submerge as much as possible.

Cancel the Sauté function. Press the Pressure Cook/Manual button and set the timer for 4 minutes (5 minutes for softer noodles).

Once the cook cycle is finished, let the pot sit undisturbed for 2 minutes, then perform a controlled Quick Release of the remaining pressure.

When the pressure pin drops, open the lid and turn on the Sauté setting again to gently heat the mixture.

In a small bowl, whisk together the flour and cold water until smooth to make a slurry. Add this to the pot and stir well to combine.

In another small bowl, temper the sour cream by mixing a few tablespoons of hot stroganoff liquid into the sour cream, then slowly add that mixture back into the pot.

Add the tempered sour cream and chopped parsley to the pot. Stir gently to incorporate and taste to adjust salt if needed.

Serve immediately, garnishing with extra sour cream and parsley as desired.