Cut the potatoes into evenly-sized chunks (about an inch or so thick), and transfer them to a large stockpot full of cold water (and 1 tablespoon salt) filled so the water line sits about 1 inch above the potatoes.
Bring the water to a boil over high heat, reduce heat to medium-high (or whatever temperature is needed to maintain the boil), and continue cooking for about 10-12 minutes, or until a fork inserted in the potato goes in easily.
Carefully drain the potatoes and add leave them to dry slightly.
While the potatoes drain, in the same pot, gently heat the butter, half and half, and milk together (Do not boil).
Add the sour cream and mash the drained potatoes into the butter mixture with a ricer or potato masher. Combine by gently stirring with a wooden spoon or spatula to incorporate. The potatoes will gradually absorb the liquid and turn into a creamy mixture.
Add more butter, or half and half a little at a time, until it reaches your desired consistency and creaminess. Taste for seasoning and add salt as needed. Serve warm.
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Notes
Cut your potatoes before cooking them. Whole potatoes won’t cook as evenly. Cut the potatoes into smaller pieces for even cooking.
Be sure to start with cold water when boiling potatoes. Using hot water can cause uneven cooking.
For ultra-smooth and creamy mashed potatoes, reach for a ricer or food mill instead of a potato masher. This will give you the silky texture you crave without any lumps.
Cook the potatoes until they are fork-tender. This will help them absorb the butter and milk mixture, which gives them a creamy texture.
Don’t use a knife to check for doneness, as a knife is sharp and can slide in easily, even when the potatoes aren’t soft enough to mash.
Be sure to mash your potatoes as soon as you canafter draining. Waiting too long could cause sticky mashed potatoes.
Leftover Mash Potatoes can dry out and need additional milk to return to their original creaminess.