Pat the chicken dry with paper towels and season generously with kosher salt inside and out. Tie the legs together with kitchen twine. Let sit 1 hour in the refrigerator to allow salt to penetrate the meat. In a large bowl or measuring cup, combine the ingredients for the white sauce. Keep a cup of the sauce for serving. Set aside.Preheat your oven to 425°F (210°C) and lightly grease a baking dish or roasting pan. Line 2 halves of garlic head, age, thyme, and onion halves in the bottom of the roasting pan and arrange chicken on top. Insert a couple onion halves, 2 halves of a garlic head, sage, and thyme into the chicken. Add some more veggies around the bird. Brush chicken generously on all sides with the white sauce and sprinkle with herbs and more black pepper.Roast chicken for 50-60 minutes, brushing chicken with the white sauce every 15-20 minutes. An instant-read thermometer inserted into the thickest part of the breast or thigh should register 165°F (73°C). As you often transfer chicken in and out of the oven for brushing, you may have to roast it a little longer to compensate the loss of temperature. Once done, let chicken rest in the roasting pan at least 20 minutes before carving to let the meat re-absorbate the juices. No worries, chicken won’t get cold and it will be the juiciest chicken you’ll ever have. Garnish with fresh thyme, sage and serve with the remaining white sauce. Enjoy!