01 - Place the peeled potato chunks into a large pot and cover with cold salted water by at least 2 inches.
02 - Bring the water to a rolling boil, then reduce to a gentle simmer. Cook uncovered for 15 to 20 minutes, or until the potatoes yield easily when pierced with a fork.
03 - Drain the potatoes thoroughly in a colander, then return them to the warm pot to allow excess moisture to evaporate.
04 - Add the butter to the hot potatoes and let sit for 1 to 2 minutes until fully melted.
05 - Using a potato masher or potato ricer, mash the potatoes until completely smooth and free of lumps.
06 - Gradually fold in the warmed milk and heavy cream, stirring gently until the mixture becomes light and creamy.
07 - Season with salt and freshly ground black pepper to taste. Stir gently until fully combined and the texture is velvety smooth.
08 - Transfer to a serving bowl and serve immediately. Top with an extra pat of butter or fresh chopped chives if desired.