Prepare the Brine: Add 2 cups of water to a saucepan and add 1.5 cups of kosher salt to the pan and heat it over medium heat. Whisk the 2 ingredients together over the heat until the salt is absorbed.
Pour the salt water into a 4 gallon bucket. Add the rest of the brine ingredients to the pot and mix until all the ingredients are combined.
Brine Turkey: Carefully place the turkey into the brine and place the pot into the fridge and let it sit overnight.
When you are ready to smoke the turkey, preheat the smoker to 225ºF.
Once the turkey has sat in the brine, remove it from the pot and discard the brine.
Place the turkey on a baking sheet in the sink and carefully rinse the turkey.
Pat the turkey try with paper towel.
Place the turkey on a clean aluminum tray and carefully place the small pieces of cold butter under the skin of the turkey.
Prepare turkey seasoning: prepare turkey seasoning by cominbing all of the spices in a mediu bowl. Mix to combine.
Season turkey: Depending on how big your bird is, you'll use around 3/4 cup of the turkey seasonoing. Sprinkle the turkey with turkey seasoning. Pat the seasoning into the turkey and be sure the turkey is covered in seasoning. It's okay if some of the seasoning falls to the bottom of your tin pan becuase those flavors will help make the gravy taste amazing.
Stuff turkey: stuff the onion, garlic, and herbs in to the center of the turkey and cover the turkey with aluminum foil. set aside.
Prepare basting liquid: Place all the ingredients for the basting liquid into a small bowl (we used a disposible tin container). Be sure the bowl can get dirty in the smoker if that's what you're using.
Finally, place the pan with they turkey into the smoker and set the basting liquid next to the turkey pan.
Smoke turkey: smoke the turkey at 225ºF for 5 hours, basting the turkey every 1.5 to 2 hours with the basting liquid.
Uncover the turkey after 5 hours and increase the heat to 250ºF and smoke for an additional 1 hour or until the internal temperature of the thickest part of the turkey (the breast) reaches 165ºF. Increasing the heat will allow the skin to crisp up.
Remove the turkey from the smoker and let it rest for 15-20 minutes before carving.
Make the gravy: Discard the onion, garlic, and sprigs of herbs from the roasting pan and add all the turkey drippings to a saucepan (you should have around 1-2 cups of liquid).
Add any leftover basting liquid (if you have any) and 1 cup of chicken broth to the saucepan and bring to a gentle boil over medium/high heat.
Once the liquid is hot, turn the heat to medium and create a cornstarch slurry. Whisk 1 tablespoon cornstarch with 2 tablespoons of the liquid from the pot until the cornstarch dissolves. Then add the slurry to the pot and whisk to combine.
Continue whisking until the gravy thickens. If the gravy doesn't reach your desired thickness, repeat with another tablespoon of cornstarch.