If time allows, pat the turkey completely dry with paper towels the night before. Season all over with kosher salt (including under the skin), place on a wire rack set over a baking sheet, and refrigerate uncovered overnight or up to 48 hours. This dry-brine step is optional but strongly recommended for the crispiest skin.

When ready to roast, remove the turkey from the refrigerator 45 minutes before cooking to take the chill off. Preheat your oven to 450°F (232°C). Position an oven rack in the lower third of the oven.

Place the turkey breast-side down on a large cutting board. Using sturdy kitchen shears, cut along both sides of the backbone from tail to neck and remove it entirely (save it for stock or gravy). You will need to cut through the ribs — use firm, confident cuts.

Flip the turkey breast-side up. Using the heel of your hand, press firmly down on the breastbone until you hear a crack and the bird lies flat. This is the key step — the flatter the bird, the more evenly it will roast.

In a small bowl, combine the softened butter, minced garlic, chopped rosemary, thyme, sage, lemon zest, 1 tsp kosher salt, and black pepper. Mix until fully combined.

Use your fingers to carefully loosen the skin over the breast meat and thighs, creating a pocket. Push generous amounts of the herb butter underneath the skin, distributing it evenly over the breast and thigh meat. Rub any remaining butter over the outside of the entire bird.

Drizzle olive oil over the skin and season the exterior lightly with additional kosher salt and pepper.

Pour the white wine (or chicken broth) into the bottom of a large roasting pan. Add the quartered onion, halved lemon, and rosemary sprigs to the pan. Place a wire rack inside the roasting pan and set the spatchcocked turkey on top, breast-side up.

Roast at 450°F for 70–90 minutes, until the skin is deeply golden and crispy and an instant-read thermometer inserted into the thickest part of the breast reads 160°F and the thighs read 165°F. If the skin begins to over-brown before the turkey is done, tent the breast loosely with foil.

Remove the turkey from the oven and tent loosely with foil. Rest for 20–30 minutes before carving. Use the pan drippings to make gravy, or serve them alongside as a jus. Carve and serve immediately.