Cut the steak into bite size pieces, about a half-inch each. Set aside.

Put the beef and sauted onion base in a heat proof measuring cup. Add boiling water and stir. Set aside.

Put the Instant Pot on saute and add the butter, caramelized onions and mushrooms. Saute the mushrooms until they start to brown. Turn the Instant Pot off.

Add the steak, pasta, dry mustard and worcestershire sauce. Stir to combine.

Add the water mixture and stir so everything is under the liquid.

Secure the lid on the Instant Pot and put it on high for 4 minutes. Let it naturally release for 5 minutes then quick release the rest of the pressure.

Stir the sour cream in. If there is a lot of liquid, put the Instant Pot on saute and add the flour. Stir until the mixture thickens. If there is not too much liquid, just put the top back on the Instant Pot and let it sit, still off, with the lid on for 5 additional minutes.

Ladle the soup into bowls and grind black pepper on the top of each bowl.

Serve with crusty bread to sop up the soup. Enjoy!