Place a pot of water on the stove and bring the water to a boil. Peel and chop the potatoes into 1 inch cubes. Once the water is boiling put your potatoes in for 10 to 15 minutes or until the potatoes are soft.
Place potatoes in a large bowl; add sugar, sweet and condensed milk, 3 tablespoons of melted butter, 1/2 teaspoon salt, and vanilla. Beat with a mixer at medium speed until smooth. Add eggs; beat well. Pour potato mixture into a 13 x 9?inch baking pan coated with cooking spray.
To prepare topping, combine flour, brown sugar, and 1/8 teaspoon salt; stir with a whisk. Stir in 2 tablespoons melted butter. Sprinkle flour mixture evenly over potato mixture; arrange pecans evenly over top. Bake at 350° for 25 minutes or just until golden.
Preheat broiler (remove casserole from oven).
Broil casserole 45 seconds or until topping is bubbly. Let stand a little bit before serving.