Heat the butter in a 10-inch skillet over medium heat. Add the chicken and cook until it's well browned on both sides. Remove the chicken from the skillet.
Add the fennel and onion and cook until they're tender.
Stir the soup, milk and wine, if desired, in the skillet and heat to a boil. Reduce the heat to low. Cover and cook for 5 minutes. Return the chicken to the skillet. Cover and cook for 10 minutes or until the chicken is cooked through.