In a large pot, combine 1 gallon of water, 1 cup of kosher salt, and 1/2 cup of brown sugar.
Whisk the mixture over medium heat until the salt and sugar fully dissolve, which should take about 5 minutes.
Once dissolved, remove the brine from the heat and let it cool to room temperature. If you're short on time, you can add ice to help cool it down more quickly.
Once cooled, add the black peppercorns, allspice, ginger, smashed garlic, and bay leaves. If using, add the fresh herbs for additional flavor.
In a large container or brining bag, combine the cooled brine with your turkey, making sure it’s fully submerged. Adding ice cubes to the container can help keep the brine cold.
Seal the container or bag, and refrigerate or place in a cooler with ice packs to brine for at least 12 hours, and up to 24 hours.
After brining, remove the turkey from the brine and rinse it under cold water to remove excess salt. Pat dry with paper towels.
Proceed with seasoning and cooking your turkey as desired.