Rinse and trim the chicken. Salt and pepper chicken pieces on both sides. Lay the pieces flat, skin side up, in a glass baking dish and sprinkle with the fresh garlic, herbs, and onion. Pour vinegar and oil over the chicken, cover with plastic wrap and refrigerate. Turn the pieces once or twice while in the marinade.
Preheat the oven to 375 degrees.
Cut the potatoes 1 inch cubes for roasting. Sprinkle them with salt and pepper, coat them with olive oil. Set them aside.
Remove the chicken from the marinade, reserving the liquid. Strain the marinade through a fine sieve.
Reserve the liquid for making the gravy.
Put the potatoes on the bottom of a large roasting pan and place the chicken pieces skin side down on top of the potatoes. Bake for 30 minutes. Turn chicken skin side up and roast for an additional 45 minutes. The chicken will be golden brown with a crispy skin.
Remove chicken to a platter and cover with foil to keep warm.
Turn oven temperature up to 450 degees.
Continue to roast the potatoes in the pan for 15 -20 minutes until they are soft in the center when tested with a fork. Add the potatoes to the chicken platter. Cover with foil and keep warm.
Transfer the roasting pan to a burner on medium high heat. Deglaze the pan with the strained chicken marinade, loosening any browned bits on the bottom of the pan. Add the chicken stock and bring to a boil and cook for 5 more minutes.
Mix the cornstarch with the cold water until it is smooth and add to the sauce in the pan stirring well. Boil for 2-3 minutes, or until thickened . Ladle some of the sauce over the chicken and potatoes and place the extra sauce in a gravy boat. The masterpiece is ready to be served.
For an alternative way to thicken the sauce make a paste with 2 tablespoons of soften butter and 1 ½ TBSP of flour. Add it to the boiling sauce instead of the corn starch paste. Why should you do it? “ because some time you feel like a nut, and sometime you don’t !”.