In a large stockpot, combine 1 gallon of water, kosher salt, brown sugar, bay leaves, and peppercorns; bring to a boil, stirring until salt and sugar dissolve, then remove from heat.

Add the remaining 1 gallon of cold water to cool the brine, then add the orange halves and rosemary sprigs.

Once the brine is completely cool, submerge the turkey in the brine, ensuring it is fully covered; if needed, use a plate to keep the turkey submerged, then refrigerate for 12-24 hours.

Preheat your oven to 325°F (160°C) and remove the turkey from the brine, patting it completely dry with paper towels.

Place the turkey on a roasting rack in a pan and roast for approximately 2.5 to 3 hours, or until a meat thermometer inserted into the thickest part of the thigh reads 165°F (74°C).

Allow the turkey to rest for at least 20-30 minutes before carving to ensure the juices redistribute, resulting in a more tender and flavorful turkey.