Put the chops into a casserole. Cover with sliced kidneys and onions. Peel, core and slice the apple and put this on top. Sprinkle on the sage and season well with salt and pepper. Peel and slice the potatoes and cover the top of the dish with them. Pour on quarter of a pint water. Cover and cook at 325°F, 170°C, gas mark 3 for three hours.