Preheat your oven to 400°F (200°C). Arrange the cut sweet potatoes on a foil-lined baking sheet and roast for 45–50 minutes until tender.

Once roasted, combine sweet potatoes with melted butter, milk, brown sugar, eggs, vanilla extract, ground cinnamon, and salt in a bowl and mash until smooth.

Grease a 9×13-inch baking dish. Spoon the mashed sweet potato mixture into the dish, spreading it evenly.

In a bowl, mix all-purpose flour, brown sugar, melted butter, and chopped pecans until crumbly for the topping.

Sprinkle the pecan streusel topping over the sweet potato layer and bake at 350°F (175°C) for 20–25 minutes until golden brown.

Let the casserole cool for about 15 minutes before serving.