Pat turkey dry and let come to room temperature, about 30 minutes.
Mix softened butter with garlic, thyme, marjoram, salt, and pepper.
Rub the butter mixture generously under and over the skin.
Stuff the cavity with lemon halves and onion quarters.
Tent the breast loosely with foil and roast 1 hour 15 minutes, then remove the foil and continue roasting 1 hour to 1 hour 15 minutes, until a thermometer in the thigh reads 165°F (74°C).