Press the "Saute" button, brown the hamburger, onions, mushrooms and garlic.
Stir in cornstarch.
Add broth, soup, pepper, and ranch seasoning mix. Stir together.
Add noodles.
Cover the pot and make sure the vent on the top of the cover is set to "Sealing". Press the "Pressure Cook" or "Manual" button on high pressure. Set timer to 6 minutes. Natural release for 5 minutes and then quick release.
Carefully open lid. Stir in sour cream. Serve and top with parsley.
Notes
You can also cook the noodles separately. This is what you should do if you want to use gluten-free, whole wheat, etc. Only regular wheat noodles will cook correctly when mixed in.