• Thaw the turkey for 3 to 4 days in the fridge and then in a bucket of water on the day of roasting for a few hours until totally thawed. Rinse thoroughly and dry with paper towels.
• Remove the neck and giblet from the cavity and place in the roasting pan along with 1 cut orange, 1 cut onion, and the halved garlic bulbs. Sprinkle the turkey with salt & pepper and place it breast side up on a roasting rack over the onion, garlic, orange, and turkey parts.
• Preheat oven to 180℃ (350℉) if using a conventional oven. If you’re using force fan convection oven, preheat it to 160℃ (320℉). Set the rack at the lowest position of your oven.
• Mix the thyme and rosemary leaves with the butter and add garlic powder and salt.
• Use your fingers and carefully separate the skin from the breast. Add a tablespoon or more of herb butter under the skin of each breast. Push as far as you can push the butter.
• Then rub the rest of the herb butter all over the turkey. Sprinkle a bit more salt and black pepper over the turkey. Stuff the rest of the onion and orange quarters, and rosemary sprig in the cavity of the turkey.
• Roast for 1 hour uncovered. Then pour 2 cups of chicken broth over the turkey. Add a bay leaf in the roasting pan. Loosely cover the breasts with foil then roast the turkey for another 1 hour 20 minutes. For the last 20 min of cook time, uncover the foil to add more color to the skin. Insert a meat thermometer into the meatiest part of the thigh. It should read 74℃ (165℉). If it hasn't reached that temperature, roast for another 10 minutes. 
• Remove the turkey from the pan and place on a large platter. Let it rest 30 min before carving. Use this time to make a gravy from the pan drippings.

Gravy:

• Remove the roasting rack and carefully pour the broth from the pan through a sieve into a medium pot. In a small bowl, thoroughly whisk corn starch with room temperature water. 
• Over medium heat, slowly pour the corn starch slurry into the broth while stirring the broth. Stir until thickened. If it’s not thick enough, add more corn starch with less water, and whisk in the new batch of slurry until the gravy is thicker.