Chop mushrooms super fine or blend in a food processor. In a larger bowl, combine ground beef and mushrooms and kneed until mixed well.
Turn Instant Pot onto saute and wait until it is hot to add meat. Cook meat until no longer pink then drain off excess fat and water. Turn Instant Pot off.
Return meat to pot then add elbow noodles, broth, and all the seasoning. Don't stir but push down the noodles to make sure they are all covered.
Close Instant Pot and set to sealing position. Select manual high pressure (the manual button or the pressure cook button on the newer models) and set timer for 4 minutes.
While Instant Pot is cooking, mix milk and cornstarch together in a separate small bowl until no lumps remain.
When timer is up on the Instant Pot turn it off and perform a quick release of pressure. Turn Instant Pot back onto saute and add milk mixture. Cook for around 2 minutes (until everything starts to thicken up).
Add cheese in and stir until melted. Serve and enjoy!