Wash and peel the sweet potatoes. Place in a deep boiler, covering with water. Simmer for 60 minutes until ready for mashing. Cream the potatoes, removing all of the lumps. Add the butter, sugar, nutmeg, vanilla and eggs, mixing well. Add the baking powder to the milk, and stir into the potatoes. Pour the ingredients into pie shells and bake at 350ºF. for 50 minutes or until firm. Cool and serve. Makes 12 to 14 slices.