For the turkey, place the bird on a cutting board, breast-side down, with the legs toward you. Using kitchen shears, cut along each side of the backbone; remove. Open the turkey like a book and flip over, spreading it out on the board skin-side up. Using the palms of your hands, press firmly between the breasts to flatten. Tuck the wing tips under the breasts.
In a large saucepan, combine the cider, sugar and kosher salt. Bring to a simmer over medium-high, stirring to dissolve. Pour brine into a large bowl; add 5 to 6 big scoops of ice to chill. Line a stockpot with a turkey-size brining bag. Add the brine, stock, bourbon, herbs, spices and the turkey. Add water, if needed, to cover bird. Cover and refrigerate 1 to 2 days.
Remove the turkey from the brine; pat dry (discard the brine). Open the bird and place, skin side up, on a rack inside a large roasting pan. Rub all over with the olive oil. Let stand at room temperature 30 minutes.
For the glaze, in a small saucepan, melt the butter over medium until it foams. Add the sugar and honey, and stir until dissolved, a minute or two. Add the stock, cider, Worcestershire and bourbon; simmer at a low rolling boil until reduced to about 1/2 cup, 15-20 minutes. Let cool.
Preheat the oven to 450°F. Roast the turkey for 20 minutes. Remove from oven and baste with glaze. Return the turkey to the oven and drop the oven temperature to 400°F. Roast in 15-minute increments, basting with glaze and checking the temperature with an instant-read thermometer inserted into the thickest part of the thigh until it registers 165°F. Let rest at least 30 minutes before carving. Tilt the pan; spoon off the fat. Save the drippings for the gravy.
Melt a half stick of butter in a saucepan over medium. Whisk in pepper, flour, whiskey, and turkey drippings then the stock; simmer until thick enough to coat a spoon, about 5 minutes. Stir in Worcestershire sauce to darken the gravy and enhance the flavor.
Serve turkey with gravy alongside.