Cook the Sweet Potatoes:
Place the peeled and cubed sweet potatoes in a large pot and cover with water. Bring to a boil and cook until tender, about 15–20 minutes. Drain and return to the pot.
Mash the Sweet Potatoes:
Mash the sweet potatoes until smooth using a potato masher or hand mixer.
Mix the Sweet Potato Base:
Add melted butter, granulated sugar, milk, eggs, vanilla extract, cinnamon, nutmeg, and a pinch of salt to the mashed sweet potatoes. Mix until well combined.
Prepare the Topping:
In a mixing bowl, combine chopped pecans, brown sugar, flour, and melted butter. Stir until crumbly.
Assemble the Casserole:
Preheat your oven to 350°F (175°C). Spread the sweet potato mixture evenly into a greased 9x13-inch baking dish. Sprinkle the pecan topping evenly over the sweet potatoes.
Bake:
Bake in the preheated oven for 25–30 minutes, or until the topping is golden brown and the casserole is heated through.
Serve:
Let the casserole cool for a few minutes before serving. Enjoy it warm!