Heat the olive oil in a large skillet on med/hi. Sear the beef on all sides, a few pieces at a time without crowding the pan. Set aside. Cook the onions in the skillet until soft. Add the garlic and cook for 1 minute.
Place the beef, onion, garlic and beef stock in a large stock pot over medium heat.
Turn the heat down to low once it comes to a slight boil and simmer for 1 1/2 to 2 hours.
Add the bay leaf, thyme, vinegar, carrots, celery and potatoes to the pot. Cook on med/low until the vegetables are done. (about 45 minutes)
Remove the bay leave and any stems from the thyme.
In a small bowl, combine the flour and cold water to make a thin paste.
Turn the heat up to high and stir in the flour mixture. Cook for 1 minute, stirring constantly to thicken the broth. Season with salt and fresh ground pepper to taste.