Combine sea salt, brown sugar, and water in a large stockpot. Stir until dissolved.
Submerge the turkey in the brine, cover, and refrigerate for 12 hours or overnight.
Preheat the oven to 350°F/175°C/Gas 4.
Remove turkey from brine, rinse well, and pat dry with paper towels. Discard brine.
Brush the turkey inside and out with half the melted butter. Season the cavity with freshly ground black pepper.
Stuff with 1 onion, 2 carrots, 2 celery stalks, 1 rosemary sprig, lemon, and garlic.
Place turkey breast-side down on a roasting rack. Add remaining onions, carrots, celery, rosemary, and bay leaf to the pan. Pour in white wine.
Roast uncovered for 3½ to 4 hours.
Two-thirds through cooking, turn turkey breast-side up and brush with remaining butter.
Turkey is done at 165°F/74°C in the thickest part of the thigh and the juices run clear.
Rest for 30 minutes before carving—serve accompanied by the roasted vegetables from the pan and your favorite sides. Enjoy!