In a large saucepan of boiling water, cook the potatoes until tender, about 12 minutes; drain well.
Return the potatoes to the pan and add the goat cheese, milk, and butter; mash until smooth. Add more milk if it's not quite creamy enough for you. Mix in chopped sage and salt; season to taste with additional salt and pepper, if desired.
Mound the potatoes in a bowl. Garnish with fresh sage sprigs.
Notes
Type of potato to use? Try Russets or Yukon Gold.
I sometimes use nonfat milk and a light butter spread and they turn out just as creamy.
Make this recipe ahead if you'd like. When ready to serve, use milk to thin out the potatoes, as needed.