Brine the turkey: Combine 2 gallons water with the salt, sugar, onions, carrots, celery, garlic, rosemary, sage, coriander seeds, fennel seeds, bay leaves and crushed red pepper in a container large enough to accommodate all the ingredients and the turkey. Stir to combine. Submerge the turkey in the brine and refrigerate for 3 days.
The night before you roast the bird, remove it from the brine and pat it dry with paper towels. Make the herb butter: In a small bowl, combine the butter, rosemary, sage and some salt. Using your fingers, carefully work your way under the skin of the turkey to separate it from the breasts and legs. Massage the butter under the skin, then all over the bird. This acts like suntan lotion to create a lovely, crispy brown skin. Tie the turkey legs together with twine to keep the bird nice and compact for even cooking.
In your roasting pan, for the gravy, combine the onions, carrots, celery, garlic, thyme bundle and bay leaves. Season with salt. Plunk the turkey on top of the veggies and put it in the fridge overnight uncovered. Yes, that's right...uncovered. This allows the skin of the turkey to dry out, which will create a gorgeous brown crispy skin. Now a bunch of your prep work is out of the way, so all you have to do tomorrow is toss the turkey in the oven!
Preheat the oven to 450 degrees F. Pour the wine into the roasting pan and put the turkey in the screaming-hot oven for 35 to 40 minutes, or until it becomes beautifully browned. Reduce the heat to 350 degrees F. Baste with the pan juices and rotate the pan every 30 minutes for the remainder of the cooking time; think 17 minutes per pound...you do the math. If the turkey starts to get too brown, tent it loosely with foil.
Remove the turkey from the oven when an instant-read thermometer registers 165 degrees F when inserted into the thickest part of the thigh. (Be sure the thermometer is not touching a bone.) Transfer it to a rimmed baking sheet, cover with foil and let it rest for at least 30 minutes.
Make the gravy: Using a mesh strainer, strain the veggies out of the pan juices over a large bowl and allow the fat to rise to the top. Discard the veggies. Skim the fat from the pan juices, add it to a large saucepot and bring it to medium heat. Whisk in the flour and cook until it has the consistency of wet sand, 4 to 5 minutes. Whisk the pan juices and stock into the flour mixture. Bring to a boil and reduce to a simmer. Cook until it is thick, 10 to 15 minutes. Taste and season with salt, if needed. Carve the turkey and serve with the gravy.