Turn Instant Pot on using the saute function. Wait for the liner to get hot, then add the cooking oil, mushrooms, garlic and onion powder, salt and pepper. Cook for 2-3 minutes until the mushrooms begin to soften. Add the minced garlic, and cook for an additional 30 seconds

Pour in the beef broth to de-glaze the liner, then turn off the Instant Pot. Add the meatballs, ensuring that they are in a single layer.

Close the lid, and use the manual/high pressure button to adjust the cook time to 5 minutes (according to Instant Pot website). Meanwhile, make the cornstarch slurry by mixing the cornstarch with cold water. This is also a good time to prepare the noodles or mashed potatoes.

After the time is up, allow a 10 minute natural release before opening the valve to release any remaining pressure. Remove the lid, and turn off the Instant Pot. Use a slotted spoon to remove the meatballs, then carefully add the sour cream, Dijon mustard and Worcestershire sauce. Whisk to combine. 

Next, turn the Instant Pot on to saute, and add the cornstarch slurry. Whisk until desired thickness is reached. Return the meatballs to the sauce

Serve immediately over noodles or mashed potatoes. Garnish with fresh parsley. Store any leftovers in the refrigerator for 2-3 days in an airtight container.