Peel the potatoes and dice them into 1-inch chunks.
Add the potatoes, water, and salt to the Instant Pot.
Seal the pressure valve and cook at HIGH pressure for 6 minutes.
Quick release the pressure, then turn off the pressure cooker.
Carefully drain the cooking water from the potatoes and return them to the pot.
Add the butter, garlic powder, and black pepper, and mash the potatoes with a potato masher.
Add the milk or cream 1 tablespoon at a time while whisking the potatoes, until they are smooth and reach the consistency you like.
Scoop into a bowl, top with a little melted butter, and garnish with parsley or thinly sliced leeks.