01 - Preheat oven to 350°F. Lightly grease a 9 x 13 inch baking dish.
02 - Place sweet potatoes in a large pot, cover with water, and bring to a boil. Simmer for 15 to 20 minutes until tender, then drain thoroughly.
03 - In a large bowl, mash sweet potatoes until smooth. Stir in melted butter, milk, maple syrup or brown sugar, eggs, vanilla extract, cinnamon, nutmeg, and salt until creamy and fully combined.
04 - Spread the sweet potato mixture evenly into the prepared baking dish.
05 - Combine chopped pecans, brown sugar, flour, melted butter, cinnamon, and salt in a medium bowl until mixture is crumbly and well-coated.
06 - Sprinkle pecan streusel evenly over the sweet potato layer. Bake for 35 to 40 minutes until topping is golden brown and filling is set. Cool for at least 10 minutes before serving.