Wash, peel, and quarter the potatoes.
Add the potatoes, water, and salt to the instant pot's inner pot.
Lock the lid and set the valve to 'SEAL.'
Cook on high pressure for 8 minutes using the MANUAL +/- button. Let the pressure release naturally for a minute before turning the valve to VENT to release the steam.
Drain the water and return the potatoes to the pot. Use the SAUTE setting to remove any remaining moisture.
Add milk, butter, sour cream, salt, pepper, and mashed potatoes. Mix well.
Add parsley and melted butter, then mix vigorously with a wooden spoon.
Add the remaining butter in the center, place the lid on to keep warm and let the butter melt.
Keep warm in the instant pot on the 'KEEP WARM' setting until ready to serve.