Mix the ingredients mentioned above for Butter Mixture under the skin in a bowl. Add olive oil to prevent the butter from burning.
Season inside of the turkey with salt and pepper. Put the halved onions inside the turkey; it will give a sweet flavor. Then add the lemon, bay leaves, and a bittersweet spicy flavor. Place the turkey upright as the inside is filled.
Gently lift the skin off the turkey body, starting from the breast’s back, and gently loosen it with your fingers to create space to add the butter mixture. Undo the skin off the top of the thighs and then turn the turkey around. Undo the skin from the front of the turkey as well. Try not to tear the skin because the butter will run out during the cooking.
Take small amounts of the butter mixture formed into balls and put them under the turkey skin. Now gently pull back the skin and press down on the butter balls to spread it all around. Make sure the whole breast is covered with the butter mixture. This will keep the turkey breast moist. Use the left-over butter mixture over the top of the breast, legs, and thighs. This is best done the night before, then covering the turkey with foil and putting it in the refrigerator.
Preheat oven to 425 F.
The next day, put the turkey in a roasting pan and drizzle olive oil on top; ensure it is at room temperature before placing it in a 425 F oven for 10 mins to brown the turkey quickly.
After 10 mins, remove the turkey from the oven, then baste with the pan’s juices. Now put bacon on top of the turkey breast skin. This helps protect the turkey breast and prevents it from drying after basting turkey again with juices from the pan.
Now turn the oven temperature to 350 F. Finish cooking the turkey for 2 1/2 hours longer, basting every 45 minutes.
Test if the turkey is cooked by sticking a knife in the thigh’s bottom and see if the juices run clear. Then cover the turkey and allow it to rest for 45 mins. It might seem a long time for the turkey to rest but remember the turkey does not need to be steamy hot as you serve the turkey with hot gravy. The longer the turkey has rested, the more flavor it develops.
Remove the excess fat from the roasting pan and place the pan back on the heat. Remove the bacon strips from the top of the breast and chop them to bits. Remove the onion from the cavity, peel the skin, and dice it.
Add the bacon and onion to the baking pan. Add rosemary sprigs and chopped tomatoes. Mix well. Then add the excess trimmings from the turkey. Then pour in the dry cider to bring a lovely apple flavor. As the cider reduces, pour the resting juices from the turkey.
When the liquid has reduced by half, mash the gravy pieces to extract the most juices out n, add chicken stock and reduce again. Taste the gravy. Then sieve it. Use the back of a spoon to push it through the sieve. Pop in a sprig of rosemary and leave it to infuse. Thicken with cornstarch to desired consistency.
Add walnuts to the bottom of the gravy boat and spoon in the gravy. Now it is ready to serve with the turkey.