Place four thyme sprigs inside the chicken cavity and season the cavity with salt. Set the chicken on a plate or Sheet Pan, pat dry, and season with salt and freshly ground pepper all over. Tuck the wing tips underneath the bird and tie the drumstick ends into a tidy bundle with kitchen twine. Set the chicken aside to come to room temperature as you prep the other ingredients.

Set a large Enameled Cast Iron Skillet over medium-high heat. When the pan is hot, drizzle half the oil in and swirl, then prop the chicken against one edge of the pan to brown one outer breast and drumstick.

Add the mushrooms and leeks in a pile on the other side of the pan. Drizzle them with half of the remaining oil and season with salt and freshly ground pepper. After a few minutes, turn the vegetables so that the sides yet untouched get contact with the hot skillet. The mushrooms and leeks will become well seared in parts, deepening the overall flavor of the dish.

After browning along one edge for about 7 minutes, grasp at either end of the chicken—work carefully to avoid being burned—and flip it so the other outer breast and drumstick sit against the pan, leaning it just as you did with the first side against the pan edge.

After cooking like so until golden along that side, 3–5 minutes, turn the chicken breast side down onto the base of the pan. Add the potatoes cut sides down around the chicken, scooting the leeks and mushrooms aside and piling them on top of the potatoes as needed.

Preheat the oven to 400°F.

After 3 more minutes, turn the chicken breast side up. Add more oil to the vegetables as needed, and repeat turning the leeks, mushrooms, and potatoes so that lesser cooked elements get their turn. Add the garlic cloves, tucking them in toward the pan base to get direct contact with the hot surface. Season all with ground pepper.

After 4 or so minutes, add the wine. It will bubble vigorously. After reducing it by half, add the stock and remaining thyme sprigs. Give one last turn of the vegetables nestling all around the chicken, lifting caramelized veggies up and placing those lesser cooked down, then carefully transfer the pan to the oven to finish cooking.

Check after 25–30 minutes. Pierce the meat in between the breast and the thigh—juices should run clear—or use a meat thermometer for a temperature of 160°F (breast meat should be 155°F, overall temperature should be 165°F).

Allow the meat to rest for 10 minutes before carving with a Carving Knife.

Serve a generous pile of mushrooms, leeks, and potatoes onto each plate, along with choice pieces of chicken. Spoon the pan sauce over the top and eat at once. Save the carcass for making stock.