6 onions, halved, not peeled

1. Heat the oven to 425 degrees. Have ready a roasting pan slightly larger than the chicken and a roasting rack.

2. Generously season the chicken cavity with salt and pepper. Place the giblets, lemons and thyme in the cavity. Truss the chicken. Rub the skin with the butter. Season all over with salt and pepper.

3. Put the onions cut side down in the pan, put the rack over the onions and the chicken on its side on the rack.

4. Add about 1/2 cup water to the pan and place it mid-oven, uncovered, to roast for 20 minutes. Turn chicken to other side; roast 20 minutes more. Turn chicken breast side up to roast another 20 minutes, by which time the skin should be a deep golden color. Reduce heat to 375 degrees.

5. Turn the chicken breast side down, preferably at an angle with the head end down and tail end up, allowing juices to flow down through the breast meat. Roast until juices run clear when thigh is pierced, about 15 minutes more. Turn off oven. Transfer the chicken to a platter.

6. Season generously with salt and pepper. Cover loosely with foil. Keep warm and let rest in oven with door open and platter tilted with chicken's head end down.

7. Meanwhile, prepare the sauce: Remove onions to a platter. Put the pan over moderate heat, scraping up any bits that cling to the bottom. Cook, scraping and stirring until the liquid is almost caramelized, 2 to 3 minutes. Do not let it burn. Spoon off and discard any excess fat. Add several tablespoons cold water to deglaze pan as needed. (Hot water will cloud the sauce.) Bring to a boil. Reduce heat to low and simmer until thickened, about 5 minutes.

8. While sauce is cooking, remove the lemons, giblets and thyme from the chicken cavity. Carve the chicken into serving pieces and transfer to a warmed platter. Chop the giblets and add to the platter. Squeeze the lemons over the chicken. Place two onion halves on each plate with chicken.

9. Strain the sauce through a fine-mesh sieve and pour into a sauce boat. Serve at once with chicken.