Place all the "Pressure Cook" ingredients into the Instant Pot.
Lock the lid, point valve to Sealing and set the Instant Pot to cook at High pressure for 10 minutes. When cook time is complete, allow the pot to sit for 10 minutes Natural Pressure Release and then release any remaining pressure manually.
Carefully open the lid and use an immersion blender to purée the soup leaving some mushroom pieces whole for texture.
In a small bowl combine cream and cornstarch until smooth.
Select Saute and pour in the cream mixture, stir well, simmer lightly for a few minutes until the soup thickens.
If you would like a thicker texture, combine 2 tablespoons of water with 1 tablespoon of cornstarch in a small cup until dissolved and add the mixture to the soup. Repeat as needed. Keep in mind that the soup will thicken even more once it cools.