Put butter in the Instant Pot. Press the "Saute" button on the Instant Pot and set the time to 15 minutes.
When the butter melts, add the flour and immediately mix it with a hand-held whisk or fork until combined.
Add 2/3 cup of chicken stock and continue whisking until boiling and smooth (about 1 minute).
Add the remaining chicken stock and continue whisking until boiling, smooth and thickened (about 3 minutes).
Turn off the Instant Pot and remove the inner pot with gravy from the Instant Pot (this is to prevent it from continuing to boil in a hot pot). Add salt to taste.
Notes
This gravy can be made ahead, refrigerated and re-heated in a microwave before serving.See also: