Peel & dice parsnips & carrots. Place into a large saucepan. Cover with water. Bring water to a boil & cook for 20-25 minutes or until fork tender.
Drain water. With a potato masher, mash mixture with butter, milk, salt & pepper. Adjust seasonings as needed. You may also add more butter or milk to desired consistency. The parsnips mash better than the carrots. If a smooth consistency is desired, place mixture into a food processor & blend until smooth.