Preheat the oven to 170℃ (160℃ fan)/325°F/gas mark 3.
Cut the lemon in half and the onion into quarters and place in the body of the turkey. Stuff the neck end if desired tucking the flap of skin under the bird. Place in a roasting tin with the wings tucked under the birds.
Smear the butter all over the breast and legs of the of the turkey. Season all over with salt and pepper.
Cover the breasts of the turkey with rashers of streaky bacon. You can weave the bacon into a square first of desired, then place on top of the breast.
Calculate the cooking time and roast for the required time for a 5-6kg (12-14lb) bird it will be about 3 hours. Baste with the juices every 30 minutes. Cover the legs or the whole bird if it begins to brown too much before the end of the cooking time. The turkey is cooked when the juices run clear when a skewer or tip of a knife is inserted into the thickest part of the thigh
When cooked cover loosely with foil and leave in a warm place to rest for at least 30 minutes