Roasting this stuffed chicken at 450°, instead of at the more common 350°, makes the skin extra crispy and cuts back on the cooking time.
Preheat the oven to 450°. Spread the bread slices directly on the racks in the oven and toast for about 3 minutes, or until dry and lightly browned, turning halfway through; let cool. Tear the slices into 1/2-inch pieces and transfer to a large bowl.
In a skillet, cook the pancetta over moderate heat, turning once, until crisp, about 5 minutes. Chop the pancetta and add to the bowl with the bread.
Add the onion, celery and minced garlic to the skillet and cook, stirring frequently, until softened, about 5 minutes. Add the kale, rosemary, sage and a generous pinch each of salt and pepper and cook over moderate heat until the kale is wilted, about 3 minutes. Scrape the vegetables into the bowl with the bread.
Add 2 cups of the broth to the skillet and boil over high heat, scraping up any browned bits, until reduced to 1 cup, about 15 minutes. Pour the broth over the bread and toss; let stand, tossing occasionally, until the stuffing is cool and evenly moistened, about 10 minutes. Season with salt and pepper.
Using your fingertips, loosen the chicken skin: begin at the tip of the breast and work your way up the breast and down the thighs. Tuck the sliced garlic under the skin. Loosely pack 1 1/2 cups of the bread stuffing into the cavity, mounding it slightly around the opening.
Set the chicken on a rack in a roasting pan and season very generously with salt and pepper. Roast the chicken for 30 minutes, or until the skin is lightly golden. Spread the carrots in the pan and roast the chicken for 1 hour longer, until it is deep golden and the juices run clear when a thigh is pierced. Transfer the chicken and carrots to a platter.
Meanwhile, spoon the remaining stuffing into a small baking dish and drizzle with 1/4 cup of the chicken stock. Bake the stuffing for about 15 minutes, or until hot and crisp on top.
Strain the chicken pan juices into a small saucepan. Set the roasting pan over high heat, add the remaining 1 cup of stock and bring to a boil, scraping up any browned bits. Strain the stock into the saucepan and boil until reduced to 3/4 cup, about 15 minutes. Spoon off any fat and season the sauce with salt and pepper. Transfer to a gravy boat and serve with the chicken and stuffing.
Make Ahead: The recipe can be prepared through Step 4 and refrigerated for 1 day.
Wine Recommendation: The salty, rich stuffing suggests a round, fruity-style Chardonnay, like the bargain 1999 Rosemount. Alternatively, consider a smooth and fruity Spanish red Rioja, like the 1993 Faustino Martinez Faustino I Gran Reserva or the inexpensive 1997 Montecillo Crianza.