Mix the remaining 1/3 cup flour, butter and sugar together in a medium bowl with fingers until the butter is worked into the flour and the mixture becomes crumbly. Add nuts, oats and salt and work into the crumbs. Top the apple mixture with the crumb mixture. Transfer to the oven and bake 15 minutes. Without opening the oven, reduce oven temperature to 325 degrees and continue baking until the apple mixture is bubbling along the edges and the topping is golden 60 to 65 minutes longer.