Preheat oven to 400 degrees.
Pierce potatoes with fork and place on baking sheet. Bake until very tender, about 1 hour.
Puree pears with 1/4 cup pear juice.
Remove potatoes from oven, scoop out inside of potatoes from skins, and place in electric mixer. Reduce oven to 350 degrees.
Add butter to potatoes; mash until smooth.
Mix in pear puree, sugar, cinnamon, and nutmeg. (Can season with salt and pepper too).
Butter a 9x13 dish, add potatoes. Bake uncovered for about 20 minutes.
(Can be made ahead, covered, and chilled prior to 2nd baking. Bring to room temperature before placing in oven).