Thaw turkey completely in the fridge, unwrapped. Allow 1 day for every 1.6kg / 4lbs of turkey. Give an extra day to completely thaw. Remove from fridge 2 hours to allow turkey to reach room temperature.
Drain the water from the turkey thoroughly. Pat dry the turkey all over with a paper towel.
Remove neck (usually from large cavity), giblets (usually in a packaged from the small neck cavity), and feathers if any.
Pre heat oven to 175 degree celsius.
Wash and cut lemons and apples into quarters. Peel and chop big onion. Peel garlic. Mince 3-4 garlic cloves (for herb butter). Cut some rosemary leaves to make 1 tbsp (for herb butter).
Melt butter. Add minced garlic, 1 tbsp cut rosemary leaves, salt and pepper and mix well to make the herb butter.
Place turkey on a roasting pan with a roasting rack. Liberally spread herb butter all over the turkey, above and below, and inside of cavity.
Stuff the large cavity with cut lemons, apples, onion, garlic, rosemary, sage, thyme, and parsley. For the small neck cavity, stuff bunch of rosemary, sage, thyme, and parsley.
Place remaining herb leaves in between the folds of the turkey wings and thighs, and under the turkey. Tuck wings under the turkey body.
Add remaining apples, garlic and onion to the bottom of roasting pan. Note I didn't add lemon as I do not want to add the sourness to the drippings. Add 3 cups of water.
Roast the turkey at 175 degree celsius for 2 hours, breast side up. Monitor to ensure the skin doesn't get burnt and water at the bottom of the pan doesn't dry up. If the water dries up, add more water to the bottom of the pan.
Use a meat thermometer to monitor the internal temperature of the turkey, insert the meat thermometer at the thickest part of the turkey at the breast, in the oven. The internal temperature should reach the recommended 74 degree celsius (165 degree farenheits).
Remove roast turkey from the oven and let it rest for 15-30 minutes before carving.