This recipe belonged to my Grandmother. She was a simple home cook. She did not care for "spicy" spices, so when she created her sweet potato pie, all you tasted was the yummy sweet potato. This recipe has been a family favorite for over 50 years and it continues to be loved by the newer generations.
In a small bowl, beat egg whites until stiff. In another bowl, cream butter and potatoes. Add sugar and egg yolks to the potato mixture and mix well. Fold in egg whites. Pour into a pie crust. Bake at 400 degrees for 30 minutes.