Heat a large cast-iron skillet over medium heat. Add the brown sugar, butter and 1 tablespoon water. Cook, stirring, until the sugar is dissolved and the mixture is bubbling. Add the apples, vanilla, salt, cinnamon and lemon juice. Mix together the cornstarch and 1 tablespoon water in a small bowl to create a slurry. Add the cornstarch mixture to the skillet and stir to combine.