Bay leaves, rosemary, and lemon zest are tucked under the skin of this turkey and gently perfume the meat with a fragrant, floral flavor. Then the roast turkey is set on fresh bay branches for a dramatic presentation.
In a bowl, combine butter and 3 tablespoons salt. Lightly pound bay leaves and two-thirds of rosemary in a mortar-and-pestle (or roll over a few times in a sealed plastic bag with a rolling pin), keeping leaves intact.
Using your fingers, separate turkey skin from breasts and legs. Rub half of butter mixture under skin. Tuck bay-rosemary mixture and lemon zest evenly under skin. Season both cavities with salt; stuff with all but 3 sprigs thyme and all but 3 sprigs remaining rosemary. Rub outside of turkey all over with remaining butter mixture. Transfer turkey to a roasting pan lined with a rack and refrigerate, uncovered, at least 24 hours and up to 2 days. Bring to room temperature 1 to 2 hours before roasting.
Preheat oven to 350°F, with rack in lower third. Prick whole lemons all over with the tines of a fork. Stuff 2 lemons into larger cavity, along with 1 head garlic; tie legs with kitchen twine. Stuff remaining lemon into neck cavity. Pour 1 cup stock into pan. Add remaining 1 head garlic.
Roast turkey 1 hour. Continue roasting, basting every 20 minutes, until a thermometer inserted in thickest part of thigh (near but not touching bone) registers 165°, 1 hour, 30 minutes to 2 hours, 30 minutes more, depending on size. If pan becomes dry during roasting, add more stock, 1/2 cup at a time. Transfer turkey to a carving board or platter; let stand at least 20 minutes before carving.
Meanwhile, remove rack from pan. Tilt pan and skim excess fat from drippings (or use a fat separator). Place pan across 2 burners. Carefully remove lemon from neck cavity and squeeze 1 to 2 tablespoons juice into drippings; squeeze cloves of roasted garlic from pan into drippings. Add remaining rosemary and thyme sprigs. Bring to a simmer over medium-high heat. Add 2 cups stock; boil until reduced by half and thickened slightly, 6 to 7 minutes. Season with salt and pepper and more squeezes of lemon juice to taste. Strain gravy through a fine-mesh sieve into a bowl. Carve turkey and serve with gravy.