Place sweet potatoes in a pot with water covering just over halfway.
Bring to boil, then reduce heat and simmer until fork-tender (20–40 min).
Drain, let cool slightly, then peel and transfer to large mixing bowl.
Add eggs, milk, vanilla, sugar, salt, and melted butter.
Mash, then beat on low with mixer until smooth.
Pour into a greased 9x13 or similar baking dish.
In separate bowl, mix flour, brown sugar, pecans, and butter for topping.
Sprinkle topping evenly over the casserole.
Bake at 350°F for 35–40 minutes.
Serve warm or refrigerate leftovers up to 5 days.