2 tablespoons butter, softened
2 eggs, beaten
1 cup white sugar
1 tablespoon all-purpose flour
1/2 teaspoon salt
1/2 cup milk
1/4 teaspoon baking soda
1/2 teaspoon nutmeg
Preheat oven to 350 degrees F (175 degrees C).
Mix together mashed sweet potatoes, butter or margarine, and eggs. In a separate bowl, mix together sugar, flour, and salt. Mix in spices if desired. Add to sweet potato mixture and stir well.
Mix together buttermilk and baking soda. Add to sweet potato mixture and stir well. Mix in vanilla extract. Pour filling into pastry shell.
Bake in preheated oven for 70 minutes, until set in center.