In a 4-quart Dutch oven cook garlic in hot oil for 15 seconds. Add chicken pieces. Cook about 10 minutes or until chicken is light brown, turning to brown evenly. Drain off fat. Add potatoes, carrots, celery, onions, chicken broth, wine, snipped rosemary, salt, and pepper. Bring to boiling; reduce heat. Cover and simmer for 35 minutes or until chicken is tender and no longer pink.
Transfer chicken and vegetables to a serving platter; keep warm. Measure cooking liquid; add water, if necessary, to equal 1 cup total. For sauce, stir together cold water and cornstarch; stir into reserved liquid. Return to Dutch oven. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Season to taste. Serve with chicken. If desired, garnish with rosemary.