Preheat the oven to 400 degrees F. Untruss the chicken, sit it in a roasting pan, and put the lemon halves and 2 of the rosemary sprigs into the chicken¿s cavity.
Cut each leek into 3 logs, then slice lengthwise and add to the pan. Now, remove the core and seeds of the bell peppers and slice them into strips, following their natural curves and ridges, and add these to the pan.
Tumble in the olives, and now pour the olive oil, mostly over the vegetables but a little over the chicken, too. Add the remaining rosemary sprigs to the vegetables, along with some salt and freshly ground pepper, to taste, and, using a couple of spoons or spatulas, gently toss the vegetables about to help coat them with the oil and make sure everything¿s well mixed up.
Sprinkle some salt over the chicken and put it in the oven for about 1 to 1 1/4 hours, by which time the chicken should be cooked through, and its juices running clear when you cut into the flesh with a small sharp knife at the thickest part of the thigh joint. The vegetables should be tender by now, too, and some of the leeks will be a scorched light brown in parts.
Remove the chicken to a cutting board and, while it rests (for about 10 minutes), pop the pan of veggies back in the oven, switching the oven off as you do so.
Cut the chicken up chunkily, transferring the pieces to a large warmed platter. Now take the pan back out of the oven and, with a slotted spoon or spatula, remove the vegetables to the large platter and when all is arranged to your aesthetic delight, pour over it all the bronze, highly flavored juices that have collected in the pan.
Reprinted from Nigellissima. Copyright (c) 2012 by Nigella Lawson. Published by Clarkson Potter, a division of Random House LLC. All rights reserved.