Pat the turkey dry inside and out. Season it liberally with salt. Place on a rack over a sheet pan and place in the fridge uncovered for 12 to 24 hours.
Remove the turkey from the refrigerator 30 minutes before roasting.
Combine the butter, olive oil, cilantro, sage, rosemary, thyme, and chives in a food processor and process until smooth. Season with pepper.
Preheat the oven to 430°F convection roast (or 450°F no convection).
Put the 3 cups of the chicken stock in a medium saucepan and keep warm over low heat.
Using a wooden spoon or your fingers, gently loosen the skin from the breast of the turkey (careful not to rip the skin). Rub the breast meat (under the skin) with the herb butter mixture (approximately 1.5 tablespoons/breast). Then use the remaining herb butter to rub the entire exterior of the turkey.
Place the carrots & celery on the bottom of a large roasting pan. Place the turkey on top of the vegetables, and place in the preheated oven. Roast until lightly golden brown, 30 to 40 minutes.
Reduce the heat to 335°F convection roast (or 350°F no convection). Continue roasting, basting with the warm chicken stock every 25 minutes, until an instant-read thermometer inserted in the thigh registers 165°F, about 1½ to 2 hours additional.
Remove the turkey from the oven, tent loosely with foil, and let rest 30 minutes before slicing.
Note: If you are making the garlic mashed potatoes, put the garlic in the oven the same time as the turkey.