Coat the beef with flour and pat off the excess. Heat the oil over medium heat in a large, heavy pan. Add the beef and cook, turning to brown all sides, 8 to 10 minutes. Remove beef from the pan and transfer it to a 6- to 8-quart slow-cooker.
Add the carrots, celery, and onion to the pan, along with more oil if necessary. Cook, stirring occasionally, for 4 to 5 minutes. Stir in the 6 tablespoons of flour. Add the reconstituted Kitchen Accomplice Beef Broth Concentrate
or Beef Bone Broth Concentrate
, stirring to loosen browned bits from the pan, and bring to a simmer. Whisk in the tomato paste.
Pour the broth/vegetable mixture over the beef in the slow cooker. Add the potatoes, bay leaves, and thyme and stir to combine.
Cover and cook on high for 4 to 5 hours or on low for 7 to 9 hours.
Transfer the beef and vegetables to a serving platter. Discard the bay leaves and season the remaining sauce in the slow-cooker with salt and pepper to taste. Pour the sauce over beef and vegetables to serve.