Preheat oven to 350 degree F.
Bake sweet potatoes for 1 hour in the oven on a baking sheet. When done, let cool slightly.
Peel the skin off of the potatoes and mash them well into a large bowl.
Set aside.
In a medium bowl, cream together butter, sugar, and brown sugar until light in color and very creamy.
Add the eggs, vanilla extract, ground cinnamon, nutmeg, allspice and salt to the creamed butter and sugar.
Add evaporated milk, then pour the mixture into the sweet potatoes in the large bowl.
Stir with rubber baking spatula or wooden spoon until smooth and creamy.
Pour the pie filling into unbaked pie crust.
Stir together pecan pieces, brown sugar, flour, melted butter, and spices in a bowl and sprinkle over the pies.
Bake for 60-75 minutes, or until center of pie is still slightly jiggly and the edges are set.
Let rest and cool for 15 to 30 minutes before cutting.