Prepare the Potatoes: Peel and cut the potatoes into 1-2 inch chunks.
Cook in Instant Pot: Add the potatoes, 1 cup of water, and 1 teaspoon of salt to the Instant Pot. Close the lid and set the valve to sealing.
Pressure Cook: Select the "Pressure Cook" or "Manual" setting and set the timer for 10 minutes on high pressure.
Natural Pressure Release: Allow for a natural pressure release for 5 minutes, then do a quick pressure release by carefully turning the valve to venting.
Drain and Mash: Drain any excess water from the Instant Pot. Return the potatoes to the pot and let them sit for a minute to dry slightly.
Add Mix-ins: Add the butter to the hot potatoes and let it melt completely. Mash the potatoes with a potato masher or use a ricer or hand mixer for extra smoothness.
Cream and Season: Gradually add warm milk or cream, stirring constantly, until you reach your desired consistency. Season with salt and black pepper to taste.