Cook potatoes in large pot of boiling salted water until tender, about 30 minutes. Meanwhile, bring milk, onion, and butter to boil in small saucepan over medium-high heat.
Drain potatoes and return to pot. Add hot milk mixture and mash. Add goat cheese and mash until blended. Season to taste with salt and pepper. (Can be prepared 2 hours ahead. Let stand at room temperature. Before serving, stir over low heat until heated through.)
Makes 6 servings.
SOURCE: epicurious.com