Preheat a large stock pot over medium high heat. Season chicken with salt and pepper. Add butter and oil to pot and brown chicken for 4-5 minutes. Remove to a plate. Add the diced onion and saute for 3 minutes. Add the garlic and saute for 2 more minutes, stirring occasionally. Deglaze the pot with balsamic vinegar. Return chicken and any juices to the pot. Add remaining ingredients, bring to a simmer and cook for 30 minutes.