Peel and cut the potatoes:
Peel the potatoes and cut them into even-sized chunks (about 1½ inches). This helps them cook evenly.

Boil until tender:
Place potatoes in a large pot and cover with cold water. Add a generous pinch of salt.
Bring to a boil, then reduce heat to medium and cook until the potatoes are fork-tender, about 15–20 minutes.

Drain well:
Drain the potatoes in a colander and let them sit for a minute so excess water evaporates. This keeps them fluffy, not watery.

Mash the potatoes:
Return the potatoes to the pot or a mixing bowl. Add butter and mash with a potato ricer or masher until smooth.

Add warm milk and cream:
Slowly pour in the warm milk and cream while mashing or stirring until you reach your desired consistency.
(Warming the milk helps keep the potatoes hot and prevents them from turning gummy.)

Season and serve:
Season with salt and black pepper to taste. Stir gently until creamy.
Serve immediately with a pat of butter on top.