Bake sweet potatoes at 375°F for about an hour, or until soft. Scoop out flesh when they are cool enough to handle. Mash until smooth.
Beat together butter and sugar until creamy. Stir in eggs, vanilla, cinnamon, nutmeg, ginger and salt. Mix in sweet potatoes. Add evaporated milk and blend until smooth. Pour into pie crust.
Bake in a preheated 425°F oven for 15 minutes Reduce heat to 350°F, bake for an additional 40 minutes, or until knife inserted into center comes out moist but clean. Allow to cool four hours before serving.