Rinse the turkey inside and out and pat it completely dry with paper towels. We mean REALLY, REALLY dry. (The turkey must be dry beyond a doubt, inside and out. If you’re using a frozen hen, it must first be thoroughly defrosted with no trace of ice. Any droplets of water or chips of ice can cause spattering—or worse, much worse--during frying.) Discard the bag of giblets as well as any pop-up timers or other plastic paraphernalia found in your turkey.
Trim the excess fat from around the turkey neck. Trim the tail. Fold the wings beneath the turkey as if it were lying on its back with its arms, er, wings tucked beneath its head. Truss the turkey if you like, though it's not at all necessary.
Season the turkey all over, inside and out, with salt and black pepper to taste. If desired, rub the turkey all over with the butter and, again if desired, sprinkle the turkey with the cayenne. (Do not, under any circumstances, consider stuffing the turkey.)
Situate the fryer far from your house, garage, and any other buildings or overhangs. Pour enough oil in the turkey fryer to reach the fill line, which is usually found inside the fryer about halfway between the bottom and the top. Heat the oil to 350°F (176°C). It could take an hour or more to get the oil to the proper frying temperature.
Don your apron, goggles, and gloves and have the fire extinguisher within reach. (Seriously.) Turn off the burner. Place the turkey in the fry basket and, holding the turkey away from you, slowly, slowly, slowly submerge the turkey in the hot oil. The oil will start to bubble. This is normal although at times you may need to lower the turkey an inch and then pull it back up and wait a little before lowering it again so the bubbling oil doesn't come dangerously close to the top of the fryer. The oil temperature will drop, but don't adjust the temperature just yet as it should bounce back relatively quickly.
Turn the burner back on and fry the bird until it's golden brown and an instant-read thermometer inserted in the thickest part of the thigh reads between 170°F and 180°F (76°C and 82°C). This should take about 3 minutes per pound (that's 36 minutes for a 12-pounder). Start timing the bird as soon as you plunge it into its oil bath. Maintain the temperature of the oil as best you can at 350°F (176°C) but do not cover the fryer at any point and do not allow the oil to go above 360°F (182°C). And for the love of all things good, do not leave the fryer unattended. Ever.
When the turkey is done, turn off the fryer. Line a rimmed baking sheet with brown paper bags and have someone hold it steady. Carefully, carefully, carefully lift the turkey from the fryer as if your life depended on it, because in a sense, it does. Pause, with the turkey hovering above the fryer, a few moments to allow any excess oil to drop back into the fryer. Carefully place the bird on the baking sheet. Place it on the counter, loosely cover with foil, and let it rest for at least 15 to 20 minutes. Let the oil cool completely in the fryer until after dinner.
Carve and serve as soon as possible, before you snitch so many pieces of crisp, crackly skin that your guests become wise to you. Garnish, if you please, with sage leaves or sprigs of herbs and dried figs, cranberries, or whatever else you please. Behold!
After dinner, when the oil is completely cool, pour or siphon it into empty resealable containers and dispose of it according to the rules in your city. (Don't know? Google it.)