Make the compound butter by adding all of the ingredients into a medium bowl and combining well.
Set the butter aside and start preparing the turkey.
Remove the neck and giblets from the turkey. (CKL Tip: Save the neck in the freezer for your next batch of bone broth!)
Rinse the turkey and pat it dry, inside and out, with paper towels.
Arrange the turkey breast side up, on a roasting rack inside a roasting pan.
Adjust your oven rack so the turkey will sit in the center of the oven and preheat your oven to 350°F.
Liberally salt and pepper the inside of the turkey cavity.
Place one of the quartered onions, the carrots, the celery, and 4 garlic cloves inside the cavity of the bird.
Squeeze the juice of the lemon halves into the cavity and add the lemon halves inside the cavity along with the rosemary and thyme.
Gently lift the skin of the turkey by using your fingers and going in between the skin and body of the bird.
Rub half of the compound butter under the skin of the bird, spreading the rest of the butter on top of the skin as well.
Season the skin with salt and pepper.
Tie the turkey drumsticks together with kitchen twine.
Roast the turkey for 1 1/2 - 2 hours rotating the pan 180 degrees, halfway.
Continue roasting until a thermometer inserted into into the thickest part of the turkey thigh reads 165°F and the juices run clear when the thigh is pierced.
With about 30 minutes left, add the remaining onion quarters and halved garlic cloves coated in avocado oil to the bottom of the roasting pan to use in the gravy (optional).
When the turkey is finished cooking, remove the roasting pan from the oven and let rest for 20 minutes before carving the turkey.
Remove the roasted onions, garlic cloves, and turkey drippings from pan and set aside to blend in the gravy (see recipe below).