Roast Chicken with Lemon

Pat the chicken dry and sprinkle it inside and out with the salt. Slide it inside a large resealable plastic bag and refrigerate for at least 16 hours and up to 48 hours.
Remove the chicken from the refrigerator 1 hour before roasting and place it on the counter.

Rinse the chicken inside and out under cold running water and pat the chicken very, very dry. Starting at the cavity, gently slip your fingers underneath the chicken skin and loosen it all over, reaching as far as possible into the thigh and breast area and being careful not to tear it.
Using your fingers, massage the herb butter under the skin to distribute it as evenly as possible. Slip the lemon slices under the breast skin, arranging 4 slices on each side. (If you have a small bird and the slices don't all fit, overlap them or simply tuck the extra lemon in the cavity.) Rub the chicken all over with the oil and season with the 1/2 teaspoon pepper. Bend the wing tips and tuck them under the shoulders. Don't truss the chicken.

Place a large, heavy, ovenproof skillet (preferably cast iron) in the oven and heat until very hot, about 5 minutes. Twist a 12-inch (30-centimeter) length of aluminum foil into a rope and fashion it into a ring. Remove the pan from the oven and carefully place the ring in the pan. Place the chicken, breast side up, on the ring.
Return the skillet to the oven and roast, basting occasionally with the fat in the pan, until an instant-read thermometer inserted into the thickest part of the thigh away from the bone registers 165°F (74°C), anywhere from 45 to 80 minutes, depending on the size of the bird.

Place the chicken on a rimmed platter and let stand for at least 15 minutes before carving.

While the chicken rests, remove and discard the foil ring from the skillet. Pour the pan drippings into a large heatproof liquid measuring cup. Let stand for a few minutes, then spoon off and reserve the fat floating on the surface of the drippings. Add enough stock to the drippings left in the cup to total 2 cups (16 ounces) liquid.
Place the skillet over medium heat. Add 2 tablespoons reserved fat to the skillet and whisk in the flour or cornstarch, stirring until a thick paste forms. Let the mixture bubble for 1 minute. Gradually whisk in the stock mixture and the cream and bring to a boil. Reduce the heat to low and simmer, whisking frequently, until thickened, about 3 minutes. Remove from the heat, season with salt and pepper, and add the thyme sprigs, if using.