In a quart or larger pot, combine the kosher salt, sugar, and 2 quarts cool water. Put the pot over high heat and stir occasionally until the salt and sugar dissolve. Remove from the heat and let cool. Stir in another 2 quarts of water and chill in the refrigerator.
Remove the neck, giblets and tail (if present) from the turkey: reserve them for making turkey broth. Discard the liver. Rinse the turkey well. Place the turkey breast side down in a large container. Pour the brine over the turkey. Cover with plastic wrap. Place a plate and cans to hold turkey under the brine. Refrigerate the turkey for 12 to 18 hours. Remove turkey . No need to rinse. Pat turkey dry inside and out with a paper towel. Your turkey is now ready to roast.
Preheat oven to 325 degrees. Place turkey in a roast pan, breast side down,rub with softened butter and sprinkle with pepper. Bake 3-31/2 hours or until reaches 175-180 degrees. Let rest before carving.