Read the recipe all the way through once. Keep 2–4 cups of water in a measuring cup or pitcher next to the oven. You'll add small splashes to the onions while the chicken roasts. You might not use it all, but you'll have it ready if you need it.

Grate your Gruyère from a block while the chicken roasts, so it's ready at the end. An instant-read meat thermometer is the one tool you really need. It's the only reliable way to know your chicken is done.

Preheat the oven to 425°F with a rack in the middle.

Spatchcock the chicken: "Spatchcocking" means removing the backbone so the chicken lies flat, so it cooks faster and more evenly with more crispy skin. Place the chicken breast-side down on a large cutting board, tail end facing you. Using sharp kitchen shears, cut along both sides of the backbone from the tail toward the neck and remove it (keep it if you'd like to roast it for extra flavor). Flip the chicken breast-side up and press firmly on the center of the breast with the heels of your hands until it cracks and lies flat. Tuck the wing tips behind the breasts so they don't burn. Pat the chicken very dry with paper towels. Shortcut: ask your grocery store butcher to spatchcock it for you.

Season the chicken: Slide your fingers under the skin over the breasts and thighs to gently loosen it without tearing. Rub the chicken all over with 1 tablespoon avocado oil. Generously season with kosher salt, black pepper, and your garlic-and-herb blend under the skin directly on the meat, over the skin, and on the underside. If your blend contains salt, use a little less kosher salt. No advance brining is needed. Wash your hands, cutting board, and shears with hot, soapy water after handling raw chicken.

Prepare the onions: Add the diced onions directly to the sheet pan. Drizzle with 4–5 tablespoons avocado oil, sprinkle with 1½ teaspoons kosher salt, and pour in ⅓ cup water. The water helps the onions soften before they brown, so they don't scorch early. Toss to coat, then spread them in an even layer toward the center of the pan, leaving a little space around the edges. Scatter the thyme sprigs over the top.

Set the wire rack over the onions and place the chicken skin-side up on the rack. Add the backbone to the rack too if you'd like. Roast at 425°F for about 45–60 minutes for a 4–4½ lb chicken.

After 30 minutes, check the onions, especially around the edges. If they're getting dark, add a splash of water (about ¼–½ cup), pouring it mostly around the edges to loosen the browned bits. Check every 10–15 minutes and repeat as needed. Add a little at a time so the water evaporates and the onions caramelize instead of boiling. A few dark edges are fine and add flavor; just avoid anything black. The drippings from the chicken will fall onto the onions and give them a rich, savory flavor.

The chicken is done when an instant-read thermometer reads 165°F in the thickest part of the breast and about 175°F in the thickest part of the thigh, without touching the bone.

Using oven mitts, remove the pan and carefully move the chicken to a cutting board to rest. Resting keeps the juices in the meat. Remove the rack, backbone (if using), and thyme stems. If there's a lot of fat pooled in the pan, spoon some off, leaving about 2–3 tablespoons. Reduce the oven to 400°F.

Deglaze the onions: "Deglazing" means adding liquid to a hot pan to lift the tasty browned bits stuck to the bottom. Pour the white wine over the onions and gently scrape up the browned bits with a silicone spatula, leaving behind any blackened, bitter pieces.

Add the dry orzo to the onions. Pour in the beef broth (it can be straight from the carton), then add the Dijon, Worcestershire, and heavy cream. Stir gently until the orzo is spread evenly and mostly covered by liquid. The pan will be full.

Cover the pan tightly with foil, crimping the edges so steam can't escape. The steam is what cooks the orzo. Carefully return the pan to the oven, keeping it level, and bake at 400°F for 20–25 minutes, checking at 18–20 minutes. The orzo is done when it's tender with a slight bite, most of the liquid is absorbed, and it looks creamy. If it's still firm and the pan looks dry, stir in about ½ cup water, cover, and bake a few more minutes. Lift the foil carefully, as hot steam will escape.

Remove the foil and stir in about 1 cup Gruyère, adding more to taste, until melted, rich, and creamy. No butter or extra baking needed.

While the orzo finishes, carve the chicken (it should rest at least 15–20 minutes). Cut off the legs and thighs at the joint, then the wings, then slice the breast meat. Arrange the chicken over or alongside the orzo, finish with fresh thyme and black pepper, and serve immediately.