01 - Place the peeled and chunked potatoes in a large pot. Cover with cold water by 1 inch and 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 easily pierced with a fork.
03 - Drain the potatoes completely in a colander, then return them to the pot.
04 - Set the pot over low heat for 1 to 2 minutes, allowing any residual moisture to evaporate. Gently shake the pot occasionally to prevent sticking.
05 - Using a potato masher, ricer, or food mill, mash the potatoes until completely smooth and free of lumps.
06 - Add the cubed butter to the mashed potatoes and fold gently until fully melted and evenly incorporated.
07 - Gradually pour in the warmed milk and heavy cream while 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. Transfer to a serving bowl and serve hot.