Peel and chop the potatoes into 1-inch chunks.
4 pounds russet potatoes
Place the chopped potatoes in a large pot and cover them with 2 inches of water. Bring to a boil, reduce to a simmer, and cook until the potatoes are fork-tender, about 10-15 minutes.
Drain the potatoes, letting them sit in the colander for 5 minutes to steam off any remaining water.
While the potatoes are steaming, add the heavy cream, milk, and butter to a medium saucepan. Heat over medium heat until the mixture is warm and the butter has melted.
1 cup heavy cream, 1 cup whole milk, ½ cup unsalted butter
Add the potatoes back into the pot (now off heat) or a large bowl. Mash with a potato masher until smooth.
Add in the cream/milk/butter mixture and stir until smooth. Season with salt and pepper to taste and stir.
Kosher salt and freshly ground black pepper
Serve warm with more butter and optional herbs.
Chopped fresh parsley or chives