Set your turkey out on the counter 1 to 1½ hours prior.
Tie the sage, thyme and rosemary with kitchen string and cut the garlic in half horizontally.
Move your oven rack to the lowest position and preheat your oven to 325℉ (or 160℃).
Roughly chop the carrots, celery and onion and place into the pan in an even layer. Set off to the side
Use your fingers to separate the skin from the flesh of your turkey. Using softened butter, massage it under and over the skin of the turkey, as well as the cavity.
Generously season the outside and inside of the cavity with kosher salt and freshly ground black pepper.
Place the turkey onto the vegetables and place the garlic halves and herb bundle inside the turkey cavity.
Roast for 1 hour. Remove and baste top and inside cavity with the pan drippings before returning back to the oven for another 30 minutes. Do this 2 more times or until the turkey reaches 170° when a thermometer is inserted into the thickest part of the breast. Total roasting time should be around 2 to 2-1/2 hour depending on the sized of your whole turkey breast.
Carefully transfer the turkey breast to a carving board and cover with foil.
Use a slotted spoon to remove the vegetables and discard. They have done their job.
Place the pan drippings into a fat separator. Pour the juices out and into a measuring cup (leaving the fat in the separator). Adding enough turkey broth or stock to the juices to make 4 cups
Pour 1/4 of the fat (discarding the remaining) back into the roasting pan and heat on high.
Whisk in enough flour to make a smooth paste and until a rich brown color (time will depend)*.
Continue whisking while pouring in the 4 cups of turkey broth/pan juices. Season with salt to taste.
Slice the turkey and serve with the gravy.