Warm the olive oil and brown the lamb and kidneys, then set aside.
In the same pan with the remaining meat juices and residue add the onion and half a teaspoon of salt, to draw out the moisture, and sweat for a couple of minutes.
Add the flour and coat the onions.
Add the stock, the thyme, bay leaves and Worcester sauce. Stir and make a lovely thickened gravy.
Butter a lidded casserole dish and first lay a layer of potatoes on the bottom of the dish. Add half of the lamb and kidney mixture.
To this add a layer of black pudding slices, about half will do. Pour over half the gravy.
Cover with a layer of potato slices, and as before a layer of meat then black pudding, then the gravy. Season the potatoes as you go.
The top layer of potatoes can be arranged as carefully as you like to make a nice scalloped pattern or funky circles.
Dot with butter cubes.
Cover with the lid and place in the oven, for 20 minutes, then take off the lid and cook for a further 20 minutes until the top layer of potatoes are golden.