Preheat the oven to 425°F / 220°C for standard ovens, or 390°F / 200°C for fan-assisted ovens. Make sure the shelf is moved to the lowest part of the oven.
Prepare a large baking tray with parchment paper, and a bed of 1/2 of the orange slices, 6 cloves of garlic, 1/2 of the sage, rosemary, and 1/2 of the olive oil.
Pat the turkey dry with paper towels and poke holes all over with the sharp point of a knife.
Stuff the turkey with the other half of the orange, remaining rosemary, sage, 4 cloves of garlic, and a dash of olive oil.
Whip up the garlic herb butter and spread 1/4 of it over half of the turkey. Sprinkle salt and pepper generously over the turkey.
Flip the turkey upside down (breast side down) onto the herbs and orange in the baking tray and spread with another 1/4 of the herb butter. Save the rest of the butter in the fridge. Add salt and pepper generously as before, and pour the other 1/2 of the olive oil over the bird.
Roast uncovered for 30 minutes (see notes for additional roast turkey cooking times)
Remove the turkey from the oven and turn it over so it’s now breast-side up. I had a little help with this. We used tongs and wooden spoons.
Take the remaining herb butter from the fridge and spread half of it over the turkey. We used a pastry brush but a spoon would work too. The turkey is hot and the butter will melt easily, so take extra care!
Lower the heat to 325°F / 165°C (for standard ovens), or 300°F / 150°C (fan assisted ovens), and then roast the turkey uncovered, for 1 hour.
Remove the turkey from the oven, slather it with the remaining garlic herb butter and baste it with the juices gathering in the tray. Roast it for 30 minutes and then baste the turkey before roasting it one more time for a further 20 minutes. Tip: If your roasted turkey seems to be browning quickly, tent it loosely with aluminum foil.
Turn your oven to broil and broil the turkey for up to 10 minutes. Watch it to make sure it doesn’t overcook and burn. This is optional. If you decide to skip it, bake the turkey for a further 10 minutes.
Remove the turkey from the oven and tent it with aluminum foil if you haven’t already.
Let the turkey rest for 30 minutes.