In a large stockpot, combine 1 quart of water with kosher salt, brown sugar, peppercorns, rosemary, thyme, bay leaves, and garlic.

Bring to a simmer over medium-high heat, stirring until salt and sugar are completely dissolved.

Remove from heat and stir in the remaining cold water to cool the brine to room temperature.

Remove giblets and neck from the turkey; place the bird in a large food-grade brining container or bucket.

Pour the cooled brine over the turkey until fully submerged, weighing it down with a heavy plate if necessary.

Refrigerate the turkey in the brine solution for 12 to 18 hours.

Remove turkey from the brine and discard the liquid. Pat the turkey thoroughly dry with paper towels, ensuring the skin is completely moisture-free.

Preheat oven to 325 degrees Fahrenheit (165 degrees Celsius).

Place turkey on a roasting rack in a shallow pan and brush the entire surface with softened butter.

Roast until a meat thermometer inserted into the thickest part of the thigh reaches 165 degrees Fahrenheit (74 degrees Celsius).

Transfer turkey to a carving board and allow to rest for 30 minutes before carving to allow juices to redistribute.