Prepare sweet potatoes: Put sweet potatoes in a medium saucepan and cover with water. Cook over medium-high heat until tender, 10 to 15 minutes. Drain and transfer to a large bowl. Mash drained sweet potatoes with a fork. Add eggs; mix until well combined. Add sugar, milk, butter, vanilla, and salt; mix until smooth. Transfer to a 9×13-inch baking dish.
Make topping: Mix brown sugar and flour together in a medium bowl. Cut in butter with a pastry cutter until mixture is coarse and looks like peas; don’t overmix. Stir in pecans. Sprinkle topping over sweet potato mixture. Bake in the preheated oven until topping is lightly browned, about 30 minutes.
