Bring a large pot of water to a boil. Add salt to the pot of boiling water, then bring it back to a boil.
Add potatoes to water and boil for 20 to 25 minutes until tender.
Drain water from the pot. Using a hand mixer on low, whip well until the potatoes are crumbly. Then, add half a stick of chopped butter to your pot with the potatoes.
Continue mixing well until butter is fully mixed through and potatoes are creamy. Slowly add two cups of milk and salt and pepper while whipping.
Add in melted butter if desired. Mix with spoon, then top with green onions if desired, and serve!
Secure the lid and cook on high pressure for 12 minutes.
Release the pressure naturally. Carefully remove the inside pot and drain, then return to the cooker.
Use a hand mixer on low to mash them, but be careful not to over-mix. Add in butter 1 tablespoon at a time while continuing to blend.
When the butter melts and they're completely smooth, add whole milk. Blend well, then season with salt and pepper to taste.
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Notes
Creamiest mashed potatoes: Starting with the boiled potatoes and whipping them until fluffy, then slowly adding butter and milk, makes the creamiest potatoes. You can use a hand mixer to make mashed potatoes, but for ultra creamy mashed potatoes, pass them through a potato ricer after cooking!
Make-ahead mashed potatoes: For a make-ahead mashed potatoes recipe you can prepare in the oven, follow the instructions above, then store until ready to serve (up to 3-4 days). When ready to serve, whisk an egg and brush it over the top. Bake at 350°F for 30 minutes, or until the top is slightly browned.