Dry brine the turkey (recommended): Pat the turkey breast dry. Sprinkle evenly with 1 to 1.5 teaspoons kosher salt per pound of meat and a light dusting of black pepper.
Set on a rack over a plate, uncovered, in the fridge for at least 6 hours and up to 24 hours. If short on time, salt it as early as you can; even 1 hour helps.
Bring to room temp: Take the turkey out of the fridge 30–45 minutes before roasting. This promotes even cooking.
Preheat the oven to 325°F (165°C).
Make the herb butter: In a small bowl, mix softened butter, olive oil, minced garlic, 1 tablespoon chopped fresh rosemary, 1 tablespoon chopped fresh thyme, 1 tablespoon chopped fresh sage (or 1 teaspoon each dried), lemon zest, and a pinch of smoked paprika if using. Taste and season lightly with salt and pepper. Remember: the turkey is already salted from the brine.
Prep the pan: Scatter onion, and if using, carrots and celery in a small roasting pan or baking dish.
Pour 1/2 cup broth into the pan. Set a rack over the vegetables if you have one; otherwise, rest the turkey directly on the veggies.
Season the turkey: Gently loosen the skin over the breast with your fingers, being careful not to tear it. Rub half the herb butter under the skin and the rest over the top.
Season the outside with a little extra black pepper.
Roast low and steady: Place the turkey breast skin-side up in the pan. Roast at 325°F until the thickest part of the breast reaches 155°F on an instant-read thermometer, about 60–90 minutes for a 2–3 pound bone-in breast, or 45–75 minutes for boneless. Add more broth to the pan if it dries out.
Crisp the skin (optional but great): Increase the oven to 425°F (220°C) for the last 10–12 minutes to brown and crisp the skin.
Watch closely so it doesn’t burn.
Rest: Transfer the turkey to a cutting board, tent loosely with foil, and rest 15–20 minutes. The temperature will rise to a safe 160–165°F, and the juices will redistribute for maximum tenderness.
Make a quick pan sauce (optional): Skim fat from the pan. Place the pan over medium heat, add a splash of broth or water to deglaze, and simmer 3–5 minutes.
For gravy, whisk 1 tablespoon flour with 1 tablespoon butter and whisk into the simmering liquid until slightly thickened. Season with salt, pepper, and a squeeze of lemon.
Slice and serve: Carve against the grain into 1/4-inch slices. Serve with the pan sauce, lemon wedges, and your favorite sides.