In a mixing bowl, combine the sweet potatoes, sugar, eggs, milk, salt, 1/3 cup butter and vanilla. Mix together and pour into a greased 13x9 inch baking dish.
To prepare the topping, combine in a separate bowl the brown sugar, flour, 1/3 cup melted butter and pecans. Mix together and crumble over sweet potato mixture. Bake uncovered at 350 degrees F (175 degrees C) for 35 to 45 minutes.
