Preheat your oven to 450°.
Begin by prepping your turkey. Remove it from the fridge and discard any packaging. You will also need to remove the neck and giblets that are inside the cavity. You can dispose of those or use them to make gravy. Pat the turkey dry with a paper towel to ensure there is no excess moisture.
Liberally season the turkey inside the cavity as well as outside the entire bird with salt and pepper. Let the turkey sit for 1 hour to allow the seasoning to penetrate the meat. This will result in a juicier turkey.
While the turkey rests, prepare the compound butter. Finely chop half of your rosemary bundle, half the thyme bundle and half the sage bundle. In a medium bowl, combine the salted butter and chopped herbs. Stir until fully mixed and set aside.
Next, prepare the vegetables for the cavity. Cut the onion into 6 equal pieces, quarter the lemon, and slice the entire garlic head in half, lengthwise.
Once the turkey has finished resting, pat it dry one more time to remove any moisture brought out by the salt. Using clean hands or a pastry brush, slather the turkey in compound butter. Make sure to get the butter under the skin of the breast as well, to give the turkey extra flavor. This can be done by carefully separating the skin from the meat by placing your fingers in between the meat and the skin. Add the butter under the skin, and rub it all over the surface of the turkey. Continue slathering the butter all over the entire turkey (don't forget the bottom), until there is no more butter and the turkey is completely covered.
Next, it's time to stuff the turkey, place the onions, lemons, and garlic inside the cavity of the turkey. Then truss it. This can simply be done by crossing the turkey's legs and tying the, together with kitchen twine/ Tuck the wings under the turkey (in a way that mimics a person putting their hands behind their back) then it's ready to roast.
Place buttered and trussed turkey on a roasting rack, breast side up, in a large roasting pan, and place on the middle rack of your oven. Lower the heat to 350° and cook for 2-3 hours, until the thickest part of the thigh registers 165° on an instant read thermometer. The turkey will take about 15 minutes per pound, so the roasting time will depend on the overall weight of your turkey.
Once the turkey is finished cooking, remove it from the oven and let it rest for at least 25-30 minutes before carving.
Carve and serve.