How to Make It
Preheat the oven to 375°. Season the lamb all over with salt and pepper and roll it into a neat roast. With cotton twine, tie the roast at 1 1/2-inch intervals.
In a medium enameled cast-iron casserole, heat 1 tablespoon of the oil until shimmering. Add the lamb and cook over moderately high heat until richly browned all over, about 4 minutes per side. Transfer the lamb to a plate and pour off the fat in the casserole.
Add the remaining 1 tablespoon of oil to the casserole and add the bacon. Cook over moderate heat, stirring a few times, until the bacon is lightly browned, about 3 minutes. Add the onions and cook, stirring a few times, until softened. Add the wine and boil over high heat until slightly reduced, about 2 minutes. Add the stock, thyme, garlic and bay leaf. Return the lamb to the casserole along with any accumulated juices. Cover with a sheet of parchment paper and the lid. Braise in the oven for 1 hour.
Remove the casserole from the oven and transfer the lamb to a plate. Nestle the potato slices into the cooking liquid. Turn the lamb over and set it on top of the potatoes. Replace the parchment paper and the lid and bake for 1 1/2 hours longer, until the lamb and potatoes are very tender.
Transfer the lamb to a cutting board, cover loosely with foil and let rest for 15 minutes. Discard the thyme sprigs and bay leaf and season the braising liquid with salt and pepper. Discard the strings from the roast and cut the lamb into thick slices. Serve in shallow bowls with the potatoes and braising liquid, garnished with chives.