1. Cook Potatoes: Place cut potatoes in colander. Rinse under cold water until water runs clear, about 1 minute. Drain potatoes. Fill Dutch oven with 1 inch water. Bring water to boil. Place steamer basket in Dutch oven and fill with potatoes. Reduce heat to medium and cook, covered, until potatoes are tender, 20 to 25 minutes.

2. Warm Dairy: Heat milk, butter, salt, and pepper in small saucepan over medium-low heat, whisking until smooth, about 3 minutes; cover and keep warm.

3. Whip Potatoes: Pour contents of Dutch oven into colander and return potatoes to dry pot. Stir over low heat until potatoes are thoroughly dried, about 1 minute. In bowl of stand mixer fitted with whisk attachment, break potatoes into small pieces on low speed, about 30 seconds. Add milk mixture in steady stream until incorporated. Increase speed to high and whip until potatoes are light and fluffy and no lumps remain, about 2 minutes. Serve.