How to Make It
Season the turkey inside and out with salt and pepper. Transfer to a rack set in a roasting pan and let come to room temperature.
Meanwhile, preheat the oven to 400°. In a medium saucepan, melt the butter. Whisk in the citrus zests and juices along with the garlic and minced thyme; let cool slightly. Transfer half of the citrus butter to a small bowl and refrigerate until spreadable.
Run your fingers under the breast and thigh skin to loosen it, then spread the chilled butter under the skin and over the breast and thighs. Stuff the turkey cavity with the thyme sprigs and the grapefruit, orange and lemon wedges. Dampen an 18-by-18-inch double-layer piece of cheesecloth with water and squeeze dry. Soak the cheesecloth in the remaining citrus butter and drape it over the breast and legs; pour any remaining butter on top.
Roast the turkey for about 30 minutes. Add the stock to the roasting pan and continue to roast for about 1 hour and 45 minutes longer, rotating the pan a few times, until an instant-read thermometer inserted in the inner thigh registers 165°.
Carefully peel the cheesecloth off the turkey. Transfer the turkey to a board; let rest for 30 minutes. Skim the fat off the pan juices and transfer to a gravy bowl. Carve the turkey and serve with the pan juices.