Cut the chops in 1/2 and trim off some of the excess fat. Set aside. Render down the fat on a gentle heat in a heavy pan (discard the rendered-down pieces).
Peel the onions and scrape or thinly peel the carrots (if they are young you could leave some of the green stalk on the onion and carrot). Cut the carrots into large chunks, or if they are young leave them whole. If the onions are large, cut them small, if they are small they are best left whole.
Toss the meat in the hot fat in a saucepan until it is slightly brown. Transfer the meat into a casserole, then quickly toss the onions and carrots in the fat. Build the meat, carrots and onions up in layers in the casserole, carefully season each layer with freshly ground pepper and salt. Deglaze the pan with lamb stock and pour it into the casserole. Peel the potatoes and lay them on top of the casserole, so they will steam while the stew cooks. Season the potatoes. Add a sprig of thyme, bring to a boil on top of the stove, cover and transfer to a moderate oven or allow to simmer on top of the stove until the stew is cooked, 1 to 1 1/2 hours.
When the stew is cooked, pour off the cooking liquid, degrease and reheat in another saucepan. Slightly thicken it with a little roux if you like. Check seasoning, then add chopped parsley and chives and pour it back over the stew. Bring it back up to boiling point and serve from the pot or in a large pottery dish.
Melt the butter and cook the flour in it for 2 minutes on a low heat, stirring occasionally. Use as required. Roux can be stored in a cool place and used as required or it can be made up on the spot if preferred. It will keep 2 weeks in the refrigerator.