Peel the potatoes and cut them into 2-inch chunks. Place the potatoes in a large saucepan or stock pot and pour over enough cold water to cover by about 2 inches. Set the pan over high heat and bring to a boil. Boil for 8 to 10 minutes, until the potatoes are fork tender.

Drain and transfer the potatoes to the bowl of an electric mixer. Add the butter, milk, and ranch dressing packet. Beat on medium-low speed until the butter melts and the potatoes are creamy (or leave some lumps if that's your preference).

Season to taste with salt and black pepper. Transfer to a serving bowl and, if desired, top with small pieces of butter before serving.