Roast Sweet Potatoes: Preheat oven to 400°F (200°C). Pierce sweet potatoes with a fork and roast on a foil-lined baking sheet for 50 to 60 minutes until completely tender and caramelized. Let cool until easy to handle, then slide off the skins. Measure 2 cups of packed sweet potato flesh.

Mash & Puree Smooth: Place roasted sweet potato flesh in a large mixing bowl. Beat with an electric hand mixer or stand mixer on medium speed with the softened butter for 2 minutes until silky smooth and any stringy fibers are broken down.

Whisk Custard Filling: Reduce oven temperature to 350°F (175°C). Add granulated sugar, brown sugar, evaporated milk, beaten eggs, vanilla extract, cinnamon, freshly grated nutmeg, ginger, and salt to the sweet potato mixture. Beat on medium-low speed for 1 to 2 minutes until completely uniform, velvety, and pourable.

Fill Pie Shell: Roll out pie crust into a 9-inch deep-dish pie plate, flute or crimp the edges decoratively, and prick the bottom lightly with a fork. Pour the velvety sweet potato custard into the unbaked crust, smoothing the top with a spatula.

Bake to Golden Set: Bake at 350°F (175°C) for 50 to 55 minutes, until the crust is golden brown and the custard is set around the edges with a slight, gentle jiggle in the very center. (Cover pie edges with foil after 30 minutes if browning too quickly).

Cool & Slice: Transfer pie to a wire cooling rack and cool completely to room temperature (about 2 to 3 hours). The custard will firm up into a sliceable, velvety texture. Whip heavy cream with powdered sugar and vanilla, dollop generously over slices, and dust with freshly grated nutmeg before serving!