Preheat your oven to 350°F (175°C) and grease a casserole dish with butter.

Peel and chop the sweet potatoes and boil in salted water until tender, about 15-20 minutes.

Drain and mash the sweet potatoes until smooth and creamy.

In a mixing bowl, combine mashed sweet potatoes, melted butter, maple syrup, brown sugar, eggs, milk, vanilla, cinnamon, nutmeg, and salt.

Pour the mixture into the prepared casserole dish and smooth the surface with a spatula.

In a bowl, mix flour, brown sugar, melted butter, and chopped pecans until crumbly, and sprinkle over the sweet potato mixture.

Bake for 35-40 minutes until the topping is golden brown and the casserole is heated through.

Serve warm with a drizzle of maple syrup on top if desired.