1/2 stick (4 tablespoons) unsalted butter, melted, plus more for buttering the baking dish
3 to 4 large sweet potatoes (about 1 3/4 pounds), peeled and cubed
1/2 cup milk
1/4 cup brown sugar, packed
1 teaspoon pure vanilla extract
1/2 teaspoon kosher salt
2 large eggs
1/2 cup all-purpose flour
1/2 cup brown sugar, packed
1/2 stick (4 tablespoons) unsalted butter, melted
1/4 teaspoon kosher salt
3/4 cup chopped pecans
a 2-quart baking dish