Using a heavy bottomed soup pot or dutch oven, heat oil and butter over medium heat. Add in onions and saute for 5 minutes. Add in celery, shallots and garlic. Cook 3 mintues, stirring frequently. Add in broccoli and cook 3 minutes, stirring. Add in chicken stock and use a flat wooden spoon to scrape any brown bits from the pan. Add in chicken thighs. Place lid, turn down heat and cook for 1 hour. Remove the lid. Take out the chicken and let cool enough to handle. Shred. Turn heat up to medium. To the soup. add heavy cream and cream cheese. Stir well. Add in shredded cheese. Add shredded chicken back into pot. Stir well. Taste and add salt and pepper if needed. Serve in a bowl and top with additional cheddar cheese.