Combine brown sugar, flour, nuts, butter in mixing bowl and set aside. This is the topping.Pre-heat oven for 375.Boil sweet potatoes for 30 minutes, then shock in ice water. Sit for around 1 hour.Combine sweet potatoes, sugar, salt, vanilla, eggs and butter in a mixing bowl in the order listed. Mix thoroughly for 4 minutes, medium speed.Pour mixture into buttered baking dish.Bake for 30 minutes.Put crust on and bake for another 10 minutes.Let sit for 30 minutes.Can be made the day before, just refrigerate and let sit out for 30 minutes before putting in the oven.