Add the peeled, sliced potatoes to the Instant Pot and pour in enough water to cover them, then stir in 1 teaspoon of salt. The potatoes should be submerged so they cook evenly from edge to center.

Secure the lid, set the valve to sealing, and cook on manual high pressure for 8 minutes. Once the pot reaches pressure, the timer will begin counting down.

Turn the pot off as soon as the cooking time ends and carefully quick release the pressure. This keeps the potatoes from sitting in hot water too long and getting overly soft.

Drain the potatoes thoroughly and return them to the hot pot. A little steam should rise off the potatoes, which helps excess moisture evaporate before mashing.

Add the remaining salt, pepper, garlic powder, butter, milk, and sour cream, then mash until smooth. The butter should melt quickly and the potatoes should turn creamy, soft, and evenly seasoned.

Serve right away, topped with parsley if desired. The finished potatoes should look fluffy and hold soft spoon marks.