3 quarts plus 3 cups tepid water (15 cups)
2 cups dry white wine
3 heads of garlic, halved crosswise
1/2 cup kosher salt, plus more for seasoning
2 tablespoons coarsely ground black pepper, plus more for seasoning
2 lemons, thinly sliced
1 orange, thinly sliced
9 rosemary sprigs, plus 2 teaspoons chopped rosemary
Two 3 1/2-pound chickens
1 pound olive bread, cut into 1-inch cubes
2 tablespoons bacon fat or melted butter
In a very large pot, combine the water, wine, garlic, salt, 2 tablespoons of pepper, lemons, orange and 3 rosemary sprigs. Stir to dissolve the salt. Put the chickens in the brine, breast sides down. Cover and refrigerate overnight.
Preheat the oven to 425°. Remove the chickens from the brine and pat dry. Put the chickens in a roasting pan, breast sides up. Stuff the remaining 6 rosemary sprigs in the cavities and tie the legs together. Season lightly with salt and pepper and sprinkle with the chopped rosemary. Roast for 30 minutes. Add 1/2 cup of water to the pan and roast at 375° for 1 hour and 15 minutes longer, rotating the pan, until the juices run clear.
Lift the chickens and tilt them to let the cavity juices run into the pan. Transfer the chickens to a carving board and keep warm. Increase the oven temperature to 425°. Add the olive bread cubes and the bacon fat to the pan and toss well. Spread the bread in an even layer and bake in the upper third of the oven for about 20 minutes, until crisp on top and moist underneath. Carve the chickens and serve with the olive bread panzanella.