Step 1

Position a rack in the lower third of the oven and preheat to 500 degrees F. Using a paring knife, make deep cuts, 2 inches apart, all over the lamb; rub with 2 tablespoons salt and several grinds of pepper. Transfer the lamb to a roasting pan, fat-side up. Squeeze the juice of 1 lemon on top.

Step 2

Roast the lamb until most of the fat is rendered and the skin starts to brown, about 30 minutes. Transfer to a cutting board and let rest 30 to 40 minutes. Discard the fat from the pan and set the pan aside.

Step 3

Meanwhile, trim the greens from the turnips. Cut any large turnips in half.

Step 4

Roughly chop 2 bunches scallions and transfer to a food processor. Add the parsley, dill, marjoram, celery and garlic and pulse to form a coarse paste. Holding the bone, stand the leg of lamb up and rub the paste all over it; return to the roasting pan.

Step 5

Cut the remaining 4 bunches scallions into 2-inch pieces. Scatter the scallions, turnips and tomatoes around the lamb and season with salt and pepper. Squeeze the juice of the remaining 2 lemons over the lamb and drizzle with the olive oil. Loosely cover with foil.

Step 6

Reduce the oven temperature to 350 degrees F and roast the lamb 1 hour. Uncover and continue roasting until a thermometer inserted into the thickest part registers 145 degrees F for medium, 30 to 45 more minutes. Let rest 15 minutes, then slice. Serve with the vegetables and pan juices.