One day before roasting turkey, boil 2 cups chicken stock (broth), salt, bay leaves, whole black peppercorns, cinnamon sticks and brown sugar in a saucepan over medium heat.
Simmer, stirring, until salt is dissolved. Let cool for five minutes.
Place turkey in a large pot or bucket. Add 20 cups water, salt mixture and fresh rosemary leaves.
Make sure turkey is completely submerged in water. Add more water if needed.
Cover and refrigerate for 24 hours, flipping turkey once.
Marinade:
Combine together garlic, ginger, ground cumin, garam masala, red chili powder, tomato paste, lemon juice and oil in a large bowl. Stir to make a smooth paste. Season with salt and pepper.
Spread one-third of the paste between the skin and flesh, taking care not to rip. Rub the remaining paste on to the outside of the skin throughout the entire bird. Place oranges and fresh rosemary in the turkey cavity.
Roast turkey:
Preheat oven to 220 C or 450 F with rack on lower position. Remove turkey from brine 1 hour before roasting. Pat dry inside and out. Discard brine.
Place turkey on the rack of the roasting pan. Cover turkey breasts with aluminum foil. Add diced onions and carrots to the bottom of the roasting pan.
Roast for 2 and ½ hours. Remove foil. Reduce heat to 180 C or 350F. Roast for 30 minutes or until the skin is golden and crispy. Once cooked, remove turkey from the oven and place in a serving dish.
Turkey gravy:
Place a large frying pan over medium-high heat. Add butter. When it melts, add bay leaves. Allow to crackle. Add corn flour. Cook, stirring, for 2 minutes.
Add juice from roasting pan along with the cooked vegetables. Add chicken stock (broth) and rosemary. Stir. Bring to a boil. Simmer for about 20-30 minutes or until thickened with a pouring consistency.