Heat the oven to 425°F. Pat the turkey breast thoroughly dry with paper towels, place it skin-side up in a roasting pan or oven-safe skillet, and tuck the wing tips under the breast.

Combine the softened butter, olive oil, minced garlic, rosemary, thyme, sage, lemon zest, kosher salt, and black pepper in a small bowl until evenly mixed.

Gently loosen the skin from the meat with your fingers, taking care not to tear it. Spread about two-thirds of the herb butter directly over the breast meat underneath the skin, then rub the remaining butter over the outside of the skin.

Arrange the quartered onion and optional lemon wedges around the turkey. Pour the broth into the bottom of the pan, keeping it away from the turkey skin so the skin can brown properly.

Roast at 425°F for 20 minutes. Reduce the oven temperature to 350°F and continue roasting for another 60–85 minutes, depending on the breast’s shape and thickness.

Check the thickest part of the breast with an instant-read thermometer, inserting it away from the bone. The turkey is safely cooked when it reaches 165°F; if the skin browns too quickly, loosely cover it with foil.

Transfer the turkey to a cutting board, tent it loosely with foil, and let it rest for 15–20 minutes. Carve across the breast into slices and spoon the pan juices over the meat before serving.