Preheat the oven to 400˚F; spray the rack of a roasting pan with nonstick spray. Remove the chicken giblets and neck from body cavity; refrigerate or freeze for another use. Rinse the chicken under cold running water inside and out; pat dry.
Place the lemon, onion, rosemary, thyme, and 5 of the garlic cloves in the body cavity. Place the chicken, breast side up, on the rack in the roasting pan. Roast 30 minutes; pour the broth and lemon juice over the chicken. Reduce the oven temperature to 325˚F. Roast, basting frequently, until cooked through and the juices run clear when the thigh is pierced in the thickest part, and an instant read thermometer inserted in the thigh registers 180˚F, about 1 hour longer. Transfer the chicken to a cutting board; let stand 15 minutes.
Meanwhile, mince the remaining garlic clove. Pour the pan juices into a medium saucepan, skimming off any fat and reserving 1 tablespoon of the juices in a small bowl. Dissolve the cornstarch in the reserved juices. Add the wine, minced garlic, shallot, sage, salt, and water to the saucepan; bring to a boil and boil 5 minutes. Reduce the heat to low and whisk in the dissolved cornstarch; cook, stirring constantly, until the gravy thickens, about 1 minute. Remove the lemon, onion, and herbs from the cavity and discard; carve the chicken and serve with the gravy. Remove the skin before eating.

Makes 4 Servings