Heat the oven to 150 C. Lightly pat dry the lamb and bacon between sheets of kitchen paper then transfer to a bowl. Add olive oil and season lightly, gently massaging the meat.
Place a large flameproof casserole pot over high heat, add the meat and brown in one or two batches. Remove and set aside on a plate. Reduce the heat to medium, melt in the butter, add the garlic and gently cook for 30 sec – 1 minute.
Next add the onion, celery, leek and thyme and gently fry for 10 minutes or until they have softened.
Return meat to the pot, along with one third of the potatoes and all the carrots, and stir into the stew. Cover with stock and bring to a simmer. Remove from heat and add the remaining slices of potato across the top of the stew, pressing slightly into the liquid. Dot with a little butter and give a final seasoning of sea salt and ground black pepper. Cover and place in the oven to cook for about 1-1½ hours or until the meat is tender.
Gently stir in herbs (and cream if using) whilst checking the seasoning one last time.
Serve the stew right away or leave covered overnight in the fridge for flavours to develop.