Season the beef cubes with salt and pepper. Heat olive oil in a large pot over medium-high heat. Sear the beef in batches until browned on all sides. Remove and set aside.

In the same pot, add the diced onion and cook until translucent, about 5 minutes. Stir in the garlic and cook for an additional minute.

Add the tomato paste to the pot and stir until it’s well combined with the onions and garlic. Deglaze the pot with red wine (if using) or a splash of beef broth, scraping up any browned bits from the bottom.

Return the beef to the pot. Add the carrots, potatoes, celery, beef broth, Worcestershire sauce, thyme, and bay leaves. Bring to a boil, then reduce the heat to low. Cover and simmer for 1.5 to 2 hours, or until the beef is tender.

Mix the flour and cold water in a small bowl to create a slurry. Gradually stir it into the stew and simmer for another 10 minutes until the broth thickens to your liking.

Remove the bay leaves before serving. Ladle the stew into bowls and garnish with fresh parsley if desired. Serve with crusty bread or over mashed potatoes for a complete meal.