Combine flour, salt, baking powder, and sugar in a large bowl.

Add in grated butter and work into the flour mixture with your fingers until it resembles a coarse sand.

Add in milk and oil.

With a fork or pastry blender, combine flour mixture with liquid until all is incorporated.

Place in a 9-inch pie pan and evenly press dough in pan.

Freeze crust while you prepare the filling.

Boil sweet potatoes in skin for 45 minutes or until cooked through.

Preheat oven to 350 F.

Remove skin and put potato meat in a large bowl.

With a mixer, combine the sugars, milk, eggs, nutmeg, cinnamon, and vanilla to potatoes.

Beat until smooth.

Pour into pie crust and bake for 1 hour or until knife inserted comes out clean.