Preheat oven to 375°F. Cut white pumpkin in half, scoop out seeds and strings. Rub with coconut oil and salt, place face-down on parchment-lined baking sheet. Roast for 60 minutes until tender.
Cool pumpkin completely. Scoop flesh into blender, blend until smooth. Strain through fine-mesh sieve. Measure 2 cups puree for filling.
Make crust: Combine flour, salt, and sugar. Grate in frozen butter in batches. Add ice water, knead 2-3 minutes. Form disk, wrap, refrigerate 20 minutes.
Roll dough on floured surface. Transfer to 9-inch pie dish. Create fluted edges. Refrigerate while preparing filling.
Whisk together 2 cups pumpkin puree, eggs, sweetened condensed milk, pumpkin pie spice, and salt gently. Pour into chilled crust.
Bake at 425°F for 15 minutes. Reduce to 350°F, bake 30 minutes more until center is set with slight jiggle.
Cool completely on wire rack. Refrigerate before serving. Top with whipped cream if desired.