In a 13x9 inch baking dish, whisk the vinegar, lemon juice, mustard, garlic, salt and pepper. Whisk in the oil. Add the chicken pieces and turn to coat. Cover and refrigerate, turning the chicken pieces occasionally, for at least 1 hour and up to 1 day.
Preheat the oven to 400 degrees F. Roast the chicken uncovered until just cooked through, about 45 minutes. Using tongs, transfer the chicken to a serving platter. Carefully pour the cooking liquid into a small, heavy saucepan and spoon off the excess oil from atop the cooking liquid. Combine the cornstarch and water in a small bowl. Add the cornstarch to the liquid. Boil until the liquid reduces by half and thickens slightly, about 5 minutes.
Pour the sauce over the chicken. Sprinkle the parsley over the chicken and serve.
If the chicken gets too dark too quickly, cover it with aluminum foil, taking the foil off for the last 10 minutes of roasting.
by The Savvy Kitchen