Cut the beef into large cubes, removing any visible fat. Toss the pieces in a bowl with the flour, salt, and black pepper until coated evenly. Set aside.
Roughly chop the onions, celery, and carrots into thick, uniform chunks. Halve or quarter the mushrooms so they are similar in size to the other vegetables. Cut the potatoes into large pieces and keep them submerged in cold water until needed.
Heat a heavy-based, oven-proof pot over high heat. Pour in a portion of the olive oil and sear the floured beef pieces in batches until browned on all sides. If the base becomes sticky, deglaze with a small splash of wine and scrape up the browned bits. Transfer the browned meat to a separate bowl and set aside.
Preheat the oven to 150°C. Adjust the racks so the pot can sit in the center of the oven.
Lower the heat to medium-high and add a little more olive oil to the pot. Sauté the onions, carrots, celery, thyme leaves, and bay leaves for around 5 minutes, stirring occasionally, until the onions begin to soften. Stir in the tomato passata and mushrooms, cooking for another 2–3 minutes to combine.
Pour in the red wine, bring to a simmer, and let it bubble for 2–3 minutes to allow the alcohol to evaporate. Return the beef and any juices to the pot, season generously, and add the beef broth. Ensure the contents are covered by about 3–4 cm of liquid. Bring to a boil, cover with a lid, and place in the oven.
Let the casserole cook for 3 hours, stirring once per hour.
After 3 hours, remove the pot from the oven and stir in the drained potatoes. Taste and adjust seasoning if needed. Return the pot to the oven with the lid slightly ajar and cook for another hour, or until the potatoes are tender and the sauce has thickened. If a thicker consistency is desired, remove the lid completely and cook for an additional 30 minutes, stirring occasionally.
Once done, allow the casserole to rest for 10 minutes. Mix in half of the chopped parsley, and ladle into bowls. Sprinkle with the remaining parsley and serve with slices of crusty bread.