Investigators have pinpointed the cause of a fire that destroyed a popular eastern Iowa supper club.The State Fire Marshal’s office has ruled the fire at The Lark near Tiffin was started accidentally by a burner on a stove that was left on. Damage to the restaurant is estimated at more than 700-thousand dollars. The owners of the popular supper club say they would like to rebuild, but are waiting to see how much of the damage is covered by insurance.