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 to the water.
02 - Bring the pot to a boil over medium-high heat, then reduce to a gentle simmer. Cook the potatoes until they are easily pierced with a fork, approximately 15 to 20 minutes.
03 - Drain the potatoes thoroughly in a colander, then return them to the same pot.
04 - Set the pot over low heat for 1 to 2 minutes, allowing any excess moisture to evaporate from the potatoes.
05 - Using a potato masher, ricer, or food mill, mash the potatoes until completely smooth and free of lumps.
06 - Add the cubed unsalted butter to the potatoes and fold gently until fully melted and evenly incorporated.
07 - Gradually pour in the warm milk and heavy cream, stirring continuously until the mixture reaches a silky, smooth consistency. Add additional 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.