Place the potatoes in a large saucepan with enough lightly salted water to cover. Bring to a boil, reduce heat to low, cover, and simmer 12 to 15 minutes or until the potatoes feel tender when pierced with a wooden skewer. Drain and return to pan.
Shake over low heat to dry slightly. Using an electric mixer (never a food processor, which makes potatoes gluey), beat the potatoes until smooth. Add the butter in small pieces with the salt and pepper and beat until melted. Add the milk, 1/4 cup at a time, beating until smooth.
If you want to add some variety to your mashed potatoes, mix in any of the following: 3 tablespoons pesto; 4-ounces soft goat cheese and 2 tablespoons minced scallions; 1 head Roasted Garlic; 6 sun-dried tomatoes in oil, minced; 1/2 pound kale or cabbage, cooked and chopped, and 1 to 2 tablespoons finely chopped horseradish.