For the dry brine
4½ kgturkey, with giblets removed and cavity wiped clean
3 tbsplight brown sugar
4 tbspcoarse sea salt
2 tspfreshly ground black pepper
The bird should be dry brined at least 16 hours before.
Mix the sugar, salt and freshly ground black pepper with the lemon zest and rosemary.
Season the cavity of the bird with salt and pepper then rub the brine mix all over the turkey.
Leave it in the fridge overnight.
4 tbspbutter, melted
On the day you wish to serve the bird heat the oven to 220C/430F/Gas 9.
Take the turkey out of the fridge and allow it to come to room temperature while the oven is heating up.
Wipe the excess brine off the skin and brush with melted butter.
Add rosemary and sage to the turkey’s cavity.
Put the onions in a large roasting tray. Put the turkey on a trivet or wire rack in the tray.
Cook for 30 minutes, then reduce the temperature to 200C/400F/Gas 7.
Put a square of foil over the breat of the bird to prevent dryness then put back in the oven.
Don’t open the oven door until the cooking time is up.
After 1½ hours, or when the breast temp is 70 C, remove from the oven.
To test whether the turkey is cooked, insert meat thermometer into the thickest piece of thigh. It should be about 80 C.
If it is not hot enough, cook it for another 20 minutes and test again. Leave the turkey to rest in a warm place, covered with a foil tent for at least 15 minutes before carving.
Strain the juice from the bottom of the tin into a large jug - the fat will rise to the top, leaving the aromatic turkey and onion beneath.
Skim off the fat use the juices to make a gravy or serve as it is.