01 - Place the potato chunks in a large pot and cover with cold salted water by at least 2 inches.
02 - Bring to a boil, then reduce heat and simmer uncovered for 15 to 20 minutes, or until the potatoes are fork-tender.
03 - Drain the potatoes thoroughly and 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 smooth and completely lump-free.
06 - Gradually fold in the warmed milk and heavy cream, stirring gently until the mixture is light and creamy.
07 - Season with salt and freshly ground black pepper to taste. Stir gently until fully combined and velvety smooth.
08 - Serve immediately, topped with extra butter or fresh chopped chives if desired.