In a large skillet or large saucepan, brown the chicken in the butter. Season with salt and pepper. Add the onion and garlic and cook for about 2 minutes. Deglaze with the whiskey. Add the broth and mushroom mixture, cream and mustard. Bring to a boil while stirring. Cover and simmer gently for about 45 minutes. Turn the chicken pieces over and cook uncovered for about 15 minutes or until the chicken is cooked.