Place the chopped carrots, celery, and half of the onion on the bottom of the roasting pan.
Place the other half onion, garlic halves, and lemons (cut these in half) into the cavity of the bird. You can stuff the bird with whichever aromatics you would like. I think this is a really nice combination but you could also add half an apple, herbs, or anything else your heart desires!
Mix the butter with half of each of the herbs, half of the zest, half of the mustard, and 4 cloves of the garlic. Mash the butter until it is one homogenous compound butter. Season the butter with salt and butter. Gently pull the skin away from the flesh of the breast without ripping the skin. Place the butter under the skin of the turkey and make sure to evenly distribute it all over the breast meat (but under the skin.) This will keep the bird very moist while it cooks and add all that flavor into the meat itself.
In another bowl mix the other half of the minced garlic, herbs, zest, mustard, and oil. Mix until you have a paste. Spread this mixture all over the bird. You want it to get in every little nook and cranny so no spot lacks flavor! Once the bird is covered with the herb paste, liberally season it with salt and pepper.
Place the turkey on a rack in the roasting pan. Roast the bird for about 3 hours. After about an hour if the bird starts to look dark you can tent it or loosely cover with foil. You will know the bird is done when you place a thermometer inside the bird and it has an internal temperature of 155 degrees. The turkey will have some carry-over cooking so don\'t cook it any longer then this or it will become dry!
Let the bird rest for at least 45 minutes to an hour before carving into it. It will still be hot at this point just make sure to cover it with foil!