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.
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 9inch baking pan coated with cooking spray.
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.
Preheat broiler (remove casserole from oven).
Broil casserole 45 seconds or until topping is bubbly.