In a large saucepan, cook potatoes in enough boiling water to cover for 20 to 25 minutes or until very tender. Drain; cool slightly. Remove skins.
Meanwhile, prepare Pastry for Single-Crust Pie. Line pastry with a double thickness of foil. Bake in a 450 degree F oven for 8 minutes. Remove foil. Reduce the oven temperature to 375 degrees F.
In a large bowl, beat potatoes with an electric mixer until smooth. Beat in eggs, sugar, butter, nutmeg, cinnamon, vanilla, baking powder, and salt. Stir in evaporated milk. Pour into crust. Cover edge with foil.
Bake in the 375 degree F oven for 20 minutes. Remove foil and bake for 25 to 30 minutes more or until a knife inserted near center comes out clean. Makes 8 servings.