Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish.
Peel and cube the Sweet Potatoes into uniform pieces, place them in a large pot, cover with water and bring to a boil; simmer until very tender, about 15–20 minutes.
Drain the potatoes and return them to the pot or a large bowl; mash until smooth and creamy.
While still warm, stir in the Unsalted Butter until melted and combined, then mix in the Granulated Sugar, Whole Milk, beaten Eggs, Vanilla Extract and a pinch of Kosher Salt until the filling is silky and evenly seasoned.
Transfer the sweet potato mixture to the prepared baking dish and smooth the top with a spatula.
Make the topping by combining the Light Brown Sugar, All-Purpose Flour and coarsely chopped Pecans in a bowl; stir in melted butter (use remaining unsalted butter if desired) and a small pinch of kosher salt to form a crumbly mixture.
Evenly sprinkle the pecan topping over the sweet potato layer, pressing lightly so it adheres in places but still remains crumbly on top.
Bake for 25–30 minutes until the topping is golden and the filling is set; if you want extra color, broil for 1–2 minutes while watching closely.
Remove from the oven and let the casserole rest 10 minutes before serving so the filling firms slightly and flavors meld.
