Fill Instant Pot with 1 inch of water in the bottom, maximum 1 1/2 cups water.
Peel and chop the russet potatoes.
Place potatoes in Instant Pot.
Add salt, put the lid on top of the Instant Pot, and turn to close the lid.
Set the valve to “sealing”.
Press the MANUAL button. Press the +/- button to set to 12 minutes.
Let the IP do it’s job. It will take a little while for the Instant Pot to come to pressure, at which time it will start counting down.
When it counts to zero, it should beep. At this time, turn the valve/ vent to "venting" position. Immediately turn the steam release handle back to the "sealing" position at the first sign of spattering. Quick release should ALWAYS be closely attended.
Once the pressure cooker has vented, open it, and add the milk, butter, salt and pepper to taste.
Use a potato masher to mash the potatoes right in the pot.
Source:
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