Roast & Mash: Preheat oven to 400°F (200°C). Roast whole sweet potatoes on a baking sheet for 45–60 minutes, until tender. Cool slightly, peel, and mash until smooth.
Prepare Filling: Reduce oven to 350°F (175°C). In a bowl, whisk mashed sweet potatoes, condensed milk, eggs, vanilla, spices, and salt until silky smooth.
Par-Bake Crust: Place the pie crust in a 9-inch dish. Prick the base with a fork and blind bake for 10–12 minutes. Let cool slightly.
Mix Topping: Combine chopped pecans, brown sugar, melted butter, flour (or oats), and a pinch of salt. Stir until evenly coated.
Fill & Bake: Pour the filling into the crust. Sprinkle the brown sugar pecan topping evenly over it. Bake for 45–55 minutes, or until the center has a slight jiggle.
Cool & Serve: Cool on a wire rack for 2–3 hours, then refrigerate. Serve chilled or at room temperature with whipped cream or vanilla ice cream.