Preheat oven to 350 degrees F (175 degrees C). Butter a 2 quart baking dish.
Place the sweet potatoes and their liquid in a medium saucepan, and bring to a boil. Cook 15 minutes, or until tender. Remove from heat, drain, and mash.
In a medium bowl, mix the mashed sweet potatoes, white sugar, eggs, 1/3 cup butter, milk, and vanilla extract. Spread evenly into the prepared baking dish.
In a separate bowl, mix the brown sugar, chopped pecans, flour, and 1/3 cup melted butter. Sprinkle over the sweet potato mixture.
Bake 35 minutes in the preheated oven, or until a knife inserted near the center comes out clean.
