If you have the time, do this step the day before you want to roast the turkey crown. Strip the leaves off most of the thyme, reserving a few sprigs, and mash with the garlic, lemon zest and a small pinch of salt using a pestle and mortar. Put half the mixture in a bowl, then add more salt and continue mashing. Sit the crown in a roasting tin and season with the mix, rubbing it all over the skin and under the crown. You can cover and chill the crown for up to 24 hrs at this stage. Work the butter into the remaining mix and chill this, too. If you don’t have enough time, you can do this prep on the day.
Remove the turkey crown and the flavoured butter from the fridge an hour or two before roasting. Heat oven to 200C/180C fan/gas 6. Smear the butter all over the turkey skin and roast the turkey for about 1 ½ hrs, basting every 30 mins or so until golden and cooked through – a digital cooking thermometer should read 70C when inserted in the thickest part of the breast. Leave to rest for at least 20 mins before carving.
Save the juices from the tin to add to the gravy, which can be made ahead (alternatively, make the gravy in the tin). As an optional flourish, halve more lemons and sear the cut sides in a hot pan until lightly charred. Serve the turkey crown surrounded by fresh thyme sprigs, the charred lemon halves, if you want, and stuffing balls.