Place the peeled and cut potatoes in a large pot. Cover with cold water until it’s about an inch above the potatoes. Add a generous pinch of salt.
Bring the water to a boil over medium-high heat, then reduce to a simmer. Cook the potatoes until fork-tender, about 12 to 15 minutes depending on size.
While the potatoes cook, warm the milk or cream with the butter in a small saucepan or microwave until the butter melts and the mixture is warm. If using garlic, gently heat it in the milk for a softer garlic flavor.
Drain the potatoes well and return them to the hot pot. Let them sit for a minute so excess steam evaporates; this keeps the mash from becoming watery.
Using a potato masher, ricer, or electric mixer on low, begin mashing the potatoes until mostly smooth. Add the cream cheese and continue mashing or mixing until incorporated.
Slowly add the warmed milk and butter mixture in a steady stream while stirring, until you reach your desired consistency. Taste and season with salt and black pepper.
Transfer to a serving bowl and top with chopped chives or parsley, an extra pat of butter, or a sprinkle of cracked black pepper. Serve warm.