Sweet Potato Soufflé

Preheat the oven to 400°F. Grease a 2½-quart baking dish with butter. On a foil-covered baking sheet, bake the sweet potatoes for 1 hour, or until they are soft. When cool enough to handle, peel the potatoes, place the flesh in a large mixing bowl, and mash until very smooth. Add the eggs, sugar, butter, vanilla, milk, and salt. Combine well with an electric mixer or hand mixer. Turn the mixture into the baking dish. In a medium bowl, stir together the pecans, brown sugar, flour, and butter until thoroughly combined. Spoon the mixture over the sweet potatoes, making an even layer