Preheat oven to 450 F.

Using a small paring knife, make 12 slits at equal intervals all over the lamb. Insert the halved cloves into each slit.

Rub boneless leg of lamb with olive oil and season with salt and pepper.

Place fat side up on a rack over a roasting pan. Roast for 30 minutes or until the lamb has nicely browned.

While the lamb is browning, place the rest of the ingredients in a Dutch oven.

When the lamb is finished browning, place it fat side down in the Dutch oven. Reduce oven temperature to 350 F.

Add boiling water so that the liquid level covers the bottom 1/3 of the lamb.

Add half of the gremolata.

Cover and roast for 2 hours, checking the liquid level after the first hour. Add a bit of boiling water as needed.

After 2 hours, remove the roast from the oven and turn it over. Roast for another 1 1/2 hours or until the meat pulls apart easily.

Remove the lid and roast for a further 30 minutes. This step is optional and only if you want crispy bits.

After the lamb has browned nicely, remove it from the Dutch oven and place it on the serving platter. Cover loosely with foil and let rest for 20 minutes.

While the lamb is resting, carefully remove any large bits in the sauce (onions and thyme sprigs), simmer it and thicken with a flour slurry, if desired.