Preheat the oven to 350°F. Brush a 3-1/2-quart baking dish with butter.
Trim off the excess fat from the lamb, melt the butter in a skillet and, over high heat, quickly fry the chops until lightly browned and just sealed, but not cooked through. Remove from the pan and transfer the chops to a plate.
Slice the potatoes into 1/8-inch-thick rounds and cover the base of the baking dish with about a third of the slices. Season lightly with salt and pepper. Place the chops neatly on the potatoes, scatter with the onions, carrots and thyme, season lightly and add the bay leaf. Put the remaining potato slices into the dish, neatly overlapping the very top layer. Pour in enough of the stock to come up to just under the top layer by pouring the stock down one side of the dish so that the top layer is not wet. Brush well with melted butter and season lightly with salt and pepper.
Cover with a lid or foil and bake on the middle shelf of the oven for 1 1/2 hours.
Remove the lid, then add a little more stock or water if the liquid has been taken up by the potatoes and you would like it to be more moist.
Return the dish to the oven for about 45 minutes, uncovered, or until the meat is cooked and the potato top is crisp and brown. Serve hot with green vegetables of your choice.