Preheat the oven to 180°C/375°F. Put a large lidded casserole dish in the oven to heat up.
Meanwhile, add the oil to a large frying pan and fry the cutlets on both sides to brown them off a bit. You might need to do this in stages depending on the size of your pan. Remove them from the pan with a slotted spoon and set aside.
Now soften the onions in the same pan, but not too much – four to five minutes should be enough. Don’t let them brown.
Take the hot casserole from the oven and chuck the lamb and onions into it. Stir in a couple of teaspoons of flour if you want a thicker sauce, and add the stock. Add the thyme leaves and a bit of seasoning.
Put the lid on this lot and shove it back in the oven for around 30 minutes.
Remove the casserole from the oven. Stir in the sliced carrots. Now layer the sliced potatoes over the top, so that they overlap attractively and cover the whole area.
Put the lid back on and stick it back in the oven for an hour.
Take it back out of the oven. Turn the oven up to 230°C/450°F. Dot the butter over the top of the potato layer, then put it back in the oven, without the lid on, for another 30 minutes, or until the potatoes are crisp and golden.
Serve and talk about trouble at t’ mill.