Place butter and chopped onions in the Instant Pot and turn on to the Saute setting.
Saute onions in the melted butter until softened. Add mushrooms and minced garlic and saute 1-2 minutes longer.
Sprinkle the flour over the vegetable mixture and saute one minute more.
Add steak, beef stock, salt and pepper, Dijon, and Worcestershire sauce and place the lid on the pot. Lock the lid and program the Instant Pot to “pressure cook” for 15 minutes.
When the pressure cook cycle is completed, flip the quick release valve and then open the pot when it unlocks.
Stir the dry uncooked noodles into the pot and place the lid back into the locked position. Pressure cook for 3 additional minutes.
Release the pressure manually and stir the contents. The noodles should be cooked through.
Add the sour cream and cream cheese to the instant pot and gently stir in until the cream cheese is fully melted and combined. Garnish with parsley and serve.
Do not add the noodles to the instant pot with the initial pressure cook cycle. The noodles will overcook and become soggy and break apart. The instant pot cooks the noodles with that additional 3 minute pressure cook. If you’d rather cook the noodles separately, reduce the amount of beef broth in the recipe to 1 1⁄2 cups and then stir the cooked noodles in at the end after adding all of the other ingredients.
Some people prefer their gravy with dijon mustard and Worcestershire sauce for extra flavor, but you may omit them if desired. You can substitute the sour cream with Greek yogurt if needed.
The pressure cook setting on the instant pot will make even tough cuts of meat into tender bites. You can use a less expensive cut of meat for beef stroganoff in the instant pot - flank steak and skirt steak work well.
Leftover beef stroganoff can be stored in an airtight container in the refrigerator for 2-3 days.