Boil sweet potatoes until soft all the way through. Drain and return to pot. Add sour cream, butter and salt and pepper to taste. Beat until smooth then keep lid on to retain warmth.
Brown sausage in a large skillet. When cooked through remove sausage, reserving dripping in pan. Keep sausage in a warm spot.
Add diced apples and onions to the sausage drippings. Cook until softened and onions are translucent. Remove and set aside in a warm spot.
Cook down Swiss chard in skillet (about 2-3 minutes).
In two pie pans layer cooked sausage, apples and onions, Swiss chard then mashed sweet potatoes. Top with toasted walnuts.