Toss the diced beef in plain flour, salt, and pepper.
Heat vegetable oil in a large pot over medium heat. Brown the beef in batches, ensuring each piece is well-seared. Remove and set aside.
In the same pot, add the onion and garlic, cooking until softened.
Add the carrots, celery, and mushrooms, and cook for an additional 5 minutes.
Return the beef to the pot and stir in the beef stock, tomato puree, Worcestershire sauce, and dried thyme. Season with salt and pepper.
Bring to a boil, then reduce the heat and let it simmer gently for about 1.5 hours, or until the beef is tender and the sauce has thickened.