Place the potatoes, apples and salt in a large sauce pan; add enough water to cover. Bring to a boil; cover and cook for 12 minutes or until tender.
Meanwhile, in a small skillet, cook bacon over medium heat until crisp. Remove to paper towel; drain, reserve 1 teaspoon of drippings.
In the drippings, sauté onion until tender.
Drain the potatoes and apples. Add the butter, vinegar and sugar; mash until smooth.
Top with onion, bacon and nutmeg.