Cut the tip ends off of the potatoes. Boil in a large pot of water until fork tender. Cool and peel. Mash with the stick of butter in the mixer.
Remove strings from mixture.
Stir in the milk, sugar, yolks, spices and vanilla and baking powder. Beat well.
Beat the egg whites in a separate bowl until stiff, but not dry. Fold into the potato mixture.
Pour into a 9” unbaked pie shell and bake at 350 º F. for 1 hour.