Preheat oven to 325°. In a large bowl, beat the sweet potatoes, sugar, eggs, milk, butter, salt and vanilla until smooth. Transfer to a greased 2-qt. baking dish. , In a small bowl, combine the brown sugar, pecans and flour; cut in butter until crumbly. Sprinkle over sweet potato mixture. Bake, uncovered, until a thermometer reads 160°, 45-50 minutes.