Mix all the ingredients for the dry brine in a bowl, set to one side.
Put the turkey crown on a large plate or tray, using your hands gently to prise and loosen the skin away from the turkey breast. Rub the brine all over the turkey, under the skin and on the carcass too. Put the crown into a deep dish or tray and cover loosely with foil, store in the fridge for 24 hours to let the brine do its thing.
The next day take the turkey from the fridge and leave to come to room temperature for at least 1 hour. If the turkey seems wet, pat dry with kitchen paper. Put the butter under the skin to cover the breast as evenly as possible and rub the skin with cooking oil. Put parchment paper on top of the skin and foil on top to cover.
For the air fryer: Preheat the air fryer 170ºC. Place the turkey crown in the preheated air fryer. Cook for 40 minutes. Then take the foil off and cook for a further 20 minutes. Then place the foil back on and cook for another 10-20 minutes. Use a meat thermometer to check the meat is fully cooked to 75ºC.
Once cooked, leave the turkey to rest, loosely covered with foil, for 30-40 minutes.
For the oven: Preheat the oven 170ºc fan. Place the turkey crown on a baking tray covered with parchment and foil and cook for 1 hour 20 minutes, take the foil off and cook for a further 30 minutes. Once the crown is nicely browned, check the meat. If it needs more time, cover again with foil and continue cooking until the meat reaches 75ºc on the meat thermometer or the juices run clear.
Turkey crown cooking guide in an oven :
Roast at 170°C fan (Gas 4) for approximately 20 minutes per kg, plus 60 minutes for crowns under 4kg or 80 minutes for crowns over 4kg. Always check doneness at the thickest part using a thermometer (internal temperature of 75°C) or ensure the juices run clear.
As a guide, a 3kg turkey crown will take about 2 hours 10 minutes, while a 4kg crown will take roughly 2 hours 20 minutes. Once cooked, allow the turkey to rest for 30–40 minutes before carving.