In large stock pot over medium heat, combine tea and kosher salt. Stir frequently until salt is dissolved. Add onion, lemon, garlic and rosemary. Remove from heat and let cool to room temperature.

When brine has cooled, pour into food-grade, 5-gallon plastic container. Stir in ice.

Wash and dry turkey. Remove innards. Place turkey, cavity-side up, into brine, making sure cavity gets filled. Cover and place bucket in refrigerator overnight.

Heat oven to 350° F.

Remove turkey from brine, draining excess, and pat dry. Discard excess brine.

Cook turkey 15-20 minutes per pound, or until internal temperature reaches 165° F on instant-read thermometer, reserving drippings for gravy.