In a heavy soup pot over medium heat, fry the bacon lardons until crispy. Remove and set aside.
Add the butter to the bacon grease and melt. Add the onions, leeks and endive and sauté until soft. Add the vegetable broth, apple cider, apples, thyme, salt and pepper; simmer for 20 minutes.
Stir in the balsamic vinegar and blue cheese. Remove from heat and stir in the cream, and correct for seasoning.
Serve with a hunk of bread and a salad for a filling meal.