Heat the oven to 190°C (375°F) gas 5.

Trim the chops. Season generously with freshly ground black pepper and allow them to come to room temperature. Just before cooking, season again with salt and freshly ground black pepper.

In a heavy-based frying-pan large enough to take the chops in one layer, heat 15 ml (1 tbsp) olive oil and 25 g (1 oz) butter. When foaming subsides, saute the chops for 2 - 3 minutes each side, or until lightly browned, turning them with a spatula. Remove with a slotted spoon to a plate and keep warm.

Add the thinly sliced onions to the pan and saute over a moderate heat for 10 minutes or until golden, stirring occasionally. Season with salt and freshly ground black pepper to taste. Remove with a slotted spoon to a separate plate and keep warm.

Add the remaining oil and butter to the frying-pan and saute the potatoes for 7-10 minutes, or until lightly golden, turning them constantly with a spatula. Season with salt and pepper to taste.

In a casserole large enough to take the chops in one layer, spread half the onions on the bottom, then half the sauteed potatoes. Arrange the lamb chops in a single layer over the potatoes, and cover with the remaining onions and potatoes. Arrange apple quarters, end to end and rounded side up, around the edge of the casserole.

With a wooden spoon, blend the flour into the fat remaining in the frying-pan and cook over a low heat, stirring constantly for 2 - 3 minutes, to make a pale roux. Pour in the apple juice and chicken stock, whisking vigorously to prevent lumps forming. Simmer gently for 2 minutes, season with salt and pepper to taste and pour over the lamb and vegetables in the casserole.

Sprinkle with grated Gruyere cheese and bake in the oven for 45 minutes or until the lamb is tender and the cheese is golden brown. Serve at once, from the casserole.