Preheat the oven to 400°F (205°C). Place the sweet potatoes on a baking sheet and roast for 45 to 55 minutes, or until completely tender. Let them cool slightly, then peel off the skins. Reduce the oven temperature to 350°F (175°C).
Mash or blend the roasted sweet potatoes until completely smooth. In a large mixing bowl, whisk together the sweet potato puree, melted butter, brown sugar, granulated sugar, eggs, evaporated milk, vanilla extract, cinnamon, nutmeg, ginger, and salt until the filling is creamy and well combined.
Fit the pie crust into a 9-inch pie dish and gently press it into the bottom and sides. Pour the sweet potato filling into the crust and smooth the surface with a spatula.
Bake for 45 to 50 minutes, or until the edges are set and the center has a slight wobble when gently shaken. If the crust begins to brown too quickly, loosely cover the edges with foil during the final part of baking.
Let the pie cool completely on a wire rack, then refrigerate for at least 2 hours before slicing. Serve chilled or at room temperature with whipped cream if desired.