To make brine for turkey, combine kosher salt, brown sugar, bay leaves, peppercorns, and 2 gallons water in large stockpot. Bring to boil over medium heat, stirring occasionally to dissolve salt and sugar. Remove from heat, cover, and let cool to room temperature.
Place turkey breast-down into a large plastic or stainless steel container. Cover with brine, then cover container with plastic wrap and refrigerate overnight.
Remove turkey from brine and rinse. Place on roasting rack in roasting pan, then put turkey in refrigerator for 3 to 5 hours.
Chop 3 of the sage leaves, then combine with butter and chopped thyme, parsley, garlic, and shallot. Preheat oven to 475 degrees.
In medium bowl, toss together onion, celery, rosemary, apple, remaining sage leaves, and sprigs of thyme and parsley.
Remove turkey from refrigerator and sprinkle inside of turkey with salt and pepper, then stuff onion mixture into cavity. Separate skin on breast and thighs from meat, and use hands to rub half of butter mixture between skin and turkey. Melt remaining butter and herb mixture and brush onto turkey. Season turkey with salt and pepper, then tie legs together and tuck wings underneath turkey. Return to roasting rack in roasting pan.
Place turkey in oven, then reduce temperature to 325 degrees. If breast of turkey begins to get too dark, cover with aluminum foil. Roast until thermometer inserted into deepest part of breast reaches 150 degrees and thigh registers 165 degrees. Remove from oven and let rest 20 minutes before carving.