In a bowl, combine brown sugar, flour, chopped pecans, and melted butter. Stir until crumbly.
In another large bowl, mix mashed sweet potatoes, sugar, salt, vanilla, eggs, and melted butter until smooth and creamy.
Grease a 9×13-inch baking dish. Spread the sweet potato mixture evenly. Sprinkle the pecan topping across the surface.
Preheat oven to 350°F (175°C). Bake for 30–35 minutes, or until the topping is golden brown and slightly bubbling.
Let cool for a few minutes before serving to allow flavors to meld.