01 - Place the peeled and chunked potatoes in a large pot and cover with cold water by 1 inch. Add 1 teaspoon of kosher salt.
02 - Bring the water to a boil over medium-high heat, then reduce to a simmer. Cook for 15 to 20 minutes until the potatoes are fork-tender.
03 - Drain the potatoes thoroughly and return them to the pot.
04 - Let the drained potatoes sit over low heat for 1 to 2 minutes to allow excess moisture to evaporate.
05 - Mash the potatoes using a potato masher, ricer, or food mill until completely smooth with no lumps remaining.
06 - Add the cubed unsalted butter and fold it into the potatoes until fully melted and evenly incorporated.
07 - Gradually pour in the warmed whole milk and heavy cream, stirring continuously until the mixture is silky and smooth. Add more liquid for a looser texture if desired.
08 - Season with the remaining kosher salt and freshly ground black pepper to taste. Serve immediately while hot.