Preheat oven to 350 degrees. Grease a 9x13 baking dish and set aside.
In a large bowl, combine mashed sweet potatoes, eggs, melted butter, brown sugar, milk, vanilla extract, cinnamon, and salt. Mix until well combined.
Pour sweet potato filling into prepared 9x13 pan and spread into an even layer.
In a bowl, add flour, brown sugar, melted butter, and pecans. Stir until combined (mixture will be wet and clumpy). Sprinkle topping evenly over sweet potato filling.
Bake casserole for 35-40 minutes, or until center is set and top is lightly browned.
*To cook your sweet potatoes:
In the oven: Preheat oven to 425 degrees. Scrub potatoes and prick all over with a fork. Bake 45-55 minutes, or until cooked through. Allow to cool slightly, then peel the skins off and mash.
Boil on the stove top: Peel potatoes, quarter each potato, then place in a pot of water. Bring to a boil, then simmer for 15-20 minutes, or until potatoes can be pierced through with a fork. Drain and mash.
To Make Ahead: Assemble your casserole as directed. Before baking, cover your casserole and refrigerate. On Thanksgiving day, pull out your casserole and bake as directed – adding an extra 5 minutes to account for the dish being cold.