Preheat oven to 400 degrees F (200 degrees C).

Prepare the filling by blending together the sweet potatoes, evaporated milk, 1 cup brown sugar, 1/2 cup butter, eggs, cinnamon, vanilla, salt, ginger and nutmeg. Pour filling into prepared crust.

Prepare the topping by combining the flour, 1/2 cup brown sugar, cinnamon, ginger and mace. Using a pastry knife, cut the butter into the flour mixture until coarse crumbs form. Stir in nuts.

Sprinkle topping over filling and bake at 400 degrees F (200 degrees C) for 50 minutes or until golden and a knife inserted in the center comes out clean.