Combine Kosher salt, brown sugar, peppercorns, scallions, garlic, and allspice in a saucepan. Add chicken stock and bring to a boil stirring to dissolve the salt and sugar. Remove from heat and allow to cool.
Combine the cooled mixture with remaining water in pot big enough to hold the chicken and stir well. Add quartered chicken and refrigerate overnight.
Remove chicken from brine and pat dry with towels. Season with pepper.
Wrap each piece of quartered chicken in a slice of pancetta and secure with a toothpick. In skillet heat olive oil and butter over high heat. Add chicken and brown for about 10 minutes on each side. Do not crowd or they will not brown. Transfer to plate.
Add carrots, garlic, onion, bay leaves, rosemary, and celery to pan and cook about 5 minutes. Add the wine and tomatoes. Crush the tomatoes as you place them in the pot. Add chicken and reduce heat to simmer. Cook uncovered for about 30 minutes or until chicken is no longer pink. Transfer chicken to a serving platter.
Adjust seasoning. Add parsley. Pour sauce over meat. Serve with Garlic Mashed Potatoes.