In a small bowl mix salt, pepper, parsley, garlic powder, and onion powder together, and rub it all over the chuck roast, coating the exterior.
Turn your Instant Pot to the Saute setting, and wait for it to get nice and hot. Then add olive oil to the bottom, spread it around to ensure the whole bottom is coated.
Sear your roast on all sides by using cooking tongs, and holding against the heat for 4-5 minutes per side.
Set meat aside, and add butter, mushrooms, onions, and to the pot, keeping it on the saute setting. Saute for 5-7 minutes until mushrooms are starting to brown, and onions are aromatic and tender. Add garlic and saute another minute.
Pour ½ cup beef stock into the pot, and use it to deglaze the pot. You need to use a wooden spoon and scrape all the brown bits off the bottom so the pot won’t register as burn, and will be able to come to pressure later. Plus those brown bits give this so much flavor.
Slice the chuck roast into thin slices, cutting against the grain. Toss beef in 2 Tbs of flour, coating the outsides of each piece.
Add chuck roast to the pan with the onions and mushrooms, add remaining beef stock and Worcestershire sauce. Put lid on and seal, set to “sealing”.
Cook on high pressure using the manual setting to set to cook for 13 minutes.
Let pressure release naturally for 10 minutes, then carefully release remaining pressure by turning to “venting”.
Remove lid and turn the IP back on to Saute mode.
(Note: If theres is a lot of liquid, use a ladle, remove some of the liquid from the pot, and put it in a small bowl, and use a fork to whisk 2 Tbs corn starch with the liquid to make a slurry. Add the slurry to the pot. Typically there is not too much, but sometimes the meat has more liquid than other times)
Add the sour cream into the pot, and stir well, allowing to cook until sauce is thickened to desired doneness. Taste, and add additional seasoning (salt and pepper) to preference.
Serve over cooked egg noodles, and garnish with fresh parsley.