Toast fennel seeds in a small skillet over medium heat until lightly browned. Grind seeds with mortar and pestle, spice grinder or crush with a rolling pin. Combine fennel seeds, softened butter (room temperature), salt, smoked paprika, crushed red pepper, black pepper, minced garlic and thyme. (You may want to omit salt if the turkey is brined.) Set aside at room temperature. Refrigerate on parchment if making ahead. Learn more about how to make compound butter.
Preheat the oven to 350°F. (Optional: Remove turkey from brine and thoroughly rinse inside and out with cold water.) Loosen the skin on the turkey by sliding your fingers underneath it, being careful not to tear it. Pat the bird dry inside and out with paper towel. Rub about 2 to 3 tablespoons of the seasoned butter over the entire breast under the skin. Rub additional butter mixture over the entire outside of the turkey – (if the turkey seems too wet for the butter to adhere put it in the oven for 15 minutes then baste or rub, all over with the seasoned butter.)
Place thyme sprigs and stems in the cavity of the turkey and tie the legs together with a string. Place the bird on a rack in a roasting pan breast-side down. Add 1 cup of water to the bottom of the roasting pan.
Roast turkey for 1½ hours, basting with drippings every 30 minutes. Turn the turkey over so breast side is up and continue roasting until done, basting every 30 minutes. The turkey is done when the thigh meat reaches an internal temperature of 175-180°F and the breast meat reaches an internal temperature of 165-170°F (Total roasting time approximately 3 hours). When the turkey is done, remove from the oven; let stand, loosely covered with foil for 20 to 30 minutes before carving.
You may want to brine your turkey first for a moister, more tender turkey. If so, combine 1 cup of regular table salt and 1 cup sugar in one quart of hot water and mix to dissolve. Add cold ice water to make 1½ to 2 gallons. Remove giblets and neck from the cavity of the turkey. Thoroughly rinse the turkey and place in a container or brining bag large enough to hold turkey plus brine. Pour brine over turkey so that brine covers the bird (if slightly more liquid is needed add cold water). The container must be refrigerated – either in a refrigerator or in a clean cooler with plenty of ice bags or reusable gel packs to keep it cool. Leave turkey in brine for approximately 12 hours.