Pierce potatoes several times with a fork. Bake at 375° for 1 hour or until very soft; cool slightly.
Meanwhile, bring apple cider and chopped apple to a boil in a small saucepan; reduce heat, and simmer 12 to 15 minutes or until apple is very soft (apple may begin to lose its shape). Drain apple, reserving cooking liquid. Return liquid to saucepan; simmer over medium heat for 6 to 8 more minutes or until thickened to the consistency of syrup.
Cut potatoes in half lengthwise; scoop out pulp, and place in a large bowl. Discard shells. Add cooked apple to potatoes; mash with a potato masher until blended. Add butter and next 4 ingredients; continue mashing, adding reserved cooking liquid, until potatoes are desired texture. Serve hot.