Heat the oven to 180°C (350°F) gas 4.

Cut the lamb into chops with a sharp knife, then cut away most of the fat, scraping the bones clean with the knife.

With a sharp knife, cut the lambs' kidneys in half. Remove the membrane, then snip away the centre core with scissors.

Cover the bottom of a medium-sized ovenproof casserole with a layer of overlapping potato slices, using one third of the potatoes. Season generously with salt and freshly ground black pepper. Arrange half the chops and prepared kidneys on top. Season generously with salt and freshly ground black pepper, then sprinkle over half the onion slices. Repeat the procedure, seasoning each layer with salt and freshly ground black pepper. Finish with a layer of overlapping potato slices.

Pour in the chicken stock. Cut a piece of greaseproof paper to fit the top of casserole, butter it and place it butter downward over the top layer of potatoes. Cover with a lid and bake for 1 1/2 hours.

Remove the lid and buttered paper. Dot the potatoes with butter and return to the oven for a further 30 minutes, or until the potatoes are well browned and the meat is tender. Garnish with sprigs of rosemary and serve immediately.