1. Preheat oven to 350°.
2. To prepare potatoes, place potatoes in a Dutch oven; cover with water. Bring to a boil. Reduce heat, and simmer 20 minutes or until tender; drain. Cool 5 minutes.
3. Place potatoes in a large bowl; add granulated sugar, evaporated milk, 3 tablespoons 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.
4. To prepare topping, weigh or lightly spoon flour into a dry measuring cup; level with a knife. 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.
5. Preheat broiler (remove casserole from oven).
6. Broil casserole 45 seconds or until topping is bubbly. Let stand 10 minutes before serving.