Cook the sweet potatoes: Place sweet potato chunks in a large pot, cover with water, and bring to a boil. Reduce heat and simmer until tender, about 20 minutes. Drain well.
Mash and mix: In a large bowl, mash the sweet potatoes. Stir in white sugar, milk, beaten eggs, salt, vanilla, and cinnamon until smooth. Spread mixture evenly into a greased 9x13-inch baking dish.
Prepare the topping: In a separate bowl, combine brown sugar, flour, and pecans. Pour in melted butter and stir until crumbly.
Assemble: Sprinkle the pecan topping evenly over the sweet potato mixture.
Bake: Bake uncovered at 350°F (175°C) for about 1 hour, or until the topping is golden brown and crisp.
Serve: Let cool slightly before serving warm.