How to Make It
Combine celery roots, cauliflower, potatoes, lemon juice and bay leaves in a large saucepan; add cool water to cover. Bring to a boil over high heat. Reduce heat to medium and simmer until vegetables are very tender, 20 to 22 minutes. Drain well; let stand for 3 minutes. Shake to remove any excess moisture. Discard bay leaves.
Process celery root mixture in a food processor just until smooth, about 1 minute. Stir in butter, salt, white pepper and nutmeg.