Preheat the oven to 160°C (140°C fan/Gas Mark 3).
Season 700 g stewing beef chunks with salt and freshly ground black pepper.
Heat 1 tablespoon vegetable oil in a large oven-safe casserole dish over medium-high heat.
Brown the beef in batches until golden on all sides, then remove and set aside.
Add more oil if needed, then sauté 1 large chopped onion, 2 roughly chopped carrots and 2 chopped celery sticks for 5–7 minutes until softened.
Crush in 2 cloves of garlic and cook for 1 minute until fragrant.
Sprinkle over 2 tablespoons plain flour and stir for 1 minute to coat the vegetables.
Stir in 1 tablespoon tomato puree and cook for 1 minute.
Pour in 200 ml red wine and scrape up any browned bits from the base of the pot.
Add 500 ml beef stock, bring to a gentle simmer and cook until the sauce thickens slightly.
Return the browned beef to the pot, add 1 bay leaf and a few sprigs of fresh thyme, stir and adjust seasoning with salt and pepper.
Cover with a lid and transfer to the oven; cook for 2 hours.
If using, stir in 150 g sliced mushrooms, replace the lid and cook for a further 30–45 minutes until the beef is meltingly tender and the sauce is rich and thick.
Remove the bay leaf and thyme sprigs, taste and adjust seasoning if necessary.
Serve the casserole with creamy mashed potatoes, crusty bread and steamed green vegetables.