Remove the turkey crown from the fridge an hour before cooking to allow the meat to come to room temperature.
Preheat the oven to 190C/170CFan.
Start by gently lifting the skin from the turkey breast, taking care not to tear the skin too much. Run a finger under the skin, pulling it away from the turkey flesh and forming a pocket.
After making pockets on both sides of the turkey breast, gently push the the butter under the skin and work it so that it covers as much of the turkey breast as possible.
Place the turkey crown in a roasting tray and season the skin well with salt and black pepper. Add the rosemary and sage leaves to the roasting dish to flavour the bird when basting.
Cover loosely with a large piece of kitchen foil as this will stop the skin from browning too quickly before the meat is properly cooked.
Place the tray in the oven preheated and roast for an hour with the foil on top. After one hour, remove the foil (place the foil aside for later), baste the turkey by spooning over the cooking juices from the base of the roasting tray and return to the oven.
Continue to cook the turkey according the times calculated detailed in the post above or notes section in this recipe card. Cooking times depend on the size of the turkey crown. For a 2kg crown as above, continue to roast for 40-50 minutes. Baste the turkey crown again half ways through to keep the meat tender.
The turkey is cooked when the juices run clear. Ideally check the internal temperature has reached 74C.
Remove they turkey from the oven, cover loosely with the foil and allow to rest for at least 30 minutes before carving and serving.
After resting, carve the turkey into slices and serve.