Scrub potatoes well under warm running water. Optional: Peel the potatoes for a smoother mashed potato. I like to keep the potato skins on for an added boost of fiber. Cut potatoes into 1 ½ to 2-inch pieces.
Fill a Dutch oven (or large pot) with water and bring to a boil over high heat. Once boiling, add the potatoes and cook for 10-15 minutes, or until the potatoes are fork-tender. Carefully drain the potatoes and transfer them to the bowl of a stand mixer (or return to the Dutch oven for mashing by hand).
If "mashing" with a stand-mixer: Affix the paddle attachment. Add the milk and butter to the potatoes. Start to “mash” the potatoes on low, gradually increasing speed, as needed. I use a KitchenAid 10-speed mixer and prefer to use the 2nd-speed setting (low). Continue to mix until the potatoes are almost mashed but still a little lumpy, about 30 seconds to 1 minute. Turn off the mixer. Scrape down the sides of the bowl with a spatula. Adjust flavor with salt. If the potatoes seem dry, add additional milk (1-2 tablespoons at a time) to achieve your desired creaminess. Either finish mixing by hand (for a more rustic texture), or return to mixing with the stand mixer on low (for a smoother mashed potato). If finishing with the stand mixer, keep an eye on the potatoes as they can quickly become glossy and gluey - indications the potatoes are over-mashed.
If mashing by hand: Add the milk and butter to the drained potatoes in the Dutch oven. Use a potato masher to mash until everything is combined and the potatoes reach your desired level of smoothness. Adjust flavor with salt. If the potatoes seem dry, add additional milk (1-2 tablespoons at a time) to achieve your desired creaminess.
Serve warm with optional snipped chives, extra butter, freshly-cracked black pepper, or (my family's favorite) ground horseradish. Storage: Refrigerate in an airtight container for use within 3 days.