1. Preheat oven to 425 degrees. To assure even cooking, remove chicken from the refrigerator and let it stand at room temperature for 30 minutes. If the chicken comes with a plastic pop-up thermometer, discard it; the readings are often inaccurate. After rinsing the chicken inside and out with cold running water, dry it with paper towels. Tuck the tips of the wings under the bottom to keep them from burning.

2. Place onion slices in two rows in a heavy-duty roasting pan to form a bed for the chicken. The onions will flavor the chicken and the pan juices that form the base of the gravy. To help release the lemon's essence, roll it back and forth with the palm of your hand, pressing on top; then pierce the surface all over with a fork. Put garlic, thyme, and lemon inside the chicken's cavity.

3. Set chicken on the bed of onion slices, breast-side up. Then bring legs forward, cross them, and tie them together with about 18 inches of kitchen twine. (Tying the legs is much simpler than trussing the bird, which requires tying the body.)

4. Spread butter over the entire exposed surface of the chicken to ensure even browning. Sprinkle well with salt and pepper.

5. Place the chicken in the oven; in about 30 minutes, the skin should be crisp and a deep golden-brown color, and the juices should run clear when the chicken is pierced. Check the internal temperature of the breasts and thighs with an instant-read thermometer. When ready, the reading in the deepest part of the breast should be 180 degrees; the deepest part of the thigh should be 190 degrees.

6. When the chicken is finished cooking, remove it from the pan, and transfer it to a cutting board with a well to catch the juices. Let the chicken stand at room temperature for up to 20 minutes. The juices, which rise to the surface when cooking, will settle and redistribute evenly throughout the chicken. While it rests, make the pan gravy.

7. Untie the legs of the chicken. Remove the lemon, garlic, and herbs from the cavity of the chicken; discard. Place the chicken on a serving platter, breast side up, and, using a sharp knife, carve the bird: Use a large fork to pull one of the legs away from the body. With the tip of your knife, find the joint that connects the leg to the body, and sever it. Cut the thigh away from the drumstick at the second joint. To remove the breasts, cut straight down between them, following the contour of the rib cage, until you hit the wishbone. Cut through the joint where it meets the breastbone. Serve the individual pieces, or cut the breast into thin slices for a more elegant presentation.