A fresh turkey and a simple herb butter are the keys to this speedy bird.
Arrange a rack in the bottom third of the oven; preheat to 425°. In a food processor, puree the butter and chopped herbs; season with salt and pepper. Reserve 1/4 cup of the herb butter.
Set a rack inside a roasting pan. Place the turkey, breast-side up, on the rack.
If the neck and giblets are inside the cavity of the turkey, transfer all but the liver to a medium saucepan. Add the stock, celery, and 3 cups water. Cover and bring to a simmer over low heat. Simmer the stock, stirring often, while the turkey roasts.
Pat the turkey dry with paper towels. Working from the neck of the turkey, insert your hands between the skin and the breast and thighs to release the skin. Season the turkey generously all over and inside the cavity. Rub 1/2 cup of the herb butter under the skin; smear the rest all over the outside of the bird. Stuff the herb sprigs, shallots, and lemon into the cavity. Loosely tie the legs together with kitchen twine.
Add 2 cups water to the roasting pan. Roast the turkey for 30 minutes. Reduce heat to 350°. Brush the turkey with some of the reserved herb butter. Roast the turkey, rotating the pan and brushing the skin with more herb butter every 30 minutes, until an instant-read thermometer inserted into the thickest part of a thigh registers 165° or the breast registers 160°, about 1 hour, 20 minutes to 1 hour, 40 minutes. (If the pan gets dry during roasting, add 1 cup water.) Let the turkey rest for 30 minutes to 1 hour.
Tilt the turkey so the juices from the cavity drain into the roasting pan. Transfer the turkey to a cutting board. Place the pan on the stovetop over 2 burners. Skim the fat off the top of the juices. Using a slotted spoon, remove the neck and giblets from the saucepan. In a small heatproof measuring cup, whisk 1 cup of the stock from the saucepan with the flour. Whisk the stock-and-flour mixture and the remaining stock into the roasting pan. Cook over medium-high heat, whisking often, until the gravy thickens, about 5 minutes. Strain the gravy into a large pitcher. (If desired, shred the meat from the neck and chop the giblets; add to the gravy.) Slice the turkey and transfer to a platter. Serve with the gravy.
Thanksgiving recipes for planners and procrastinators here.