Wash and peel 2 lb (about 900 g) Yukon Gold or Russet potatoes
Cut potatoes into 1-inch chunks
Place potatoes in a large pot and cover with cold water
Add 1 to 2 tsp salt to the water
Bring to a boil over high heat
Reduce to a simmer and cook 15 to 20 minutes, until very tender
Drain potatoes thoroughly
Return potatoes to the hot pot (off the heat) and let steam off 30 to 60 seconds
Mash with a potato masher or ricer
Add 1/2 to 3/4 cup (120 to 180 ml) warm milk gradually, mashing as you add
Add 4 to 8 tbsp (56 to 113 g) butter, melting and mixing until smooth
Season with salt and black pepper to taste
For extra smooth mashed potatoes, use a potato ricer and add warm milk/butter gradually
For a richer texture, stir in sour cream or cream cheese (optional)
Serve immediately