01 -
Set oven to 170°C (150°C fan) or gas mark 3. Select a large flameproof casserole dish with a tight-fitting lid.
02 -
Heat 1 tablespoon oil in the casserole dish over high heat. Dry beef pieces with paper towel, season with salt and pepper, and brown in batches until deeply coloured on all sides, without crowding. Transfer browned beef to a large plate as you work.
03 -
Add remaining oil to the dish and set to medium heat. Add sliced onions and cook for about 10 minutes, stirring occasionally, until softened and golden brown.
04 -
Sprinkle flour over the softened onions and stir for 1 to 2 minutes to cook out the raw flavour. Pour in the dark beer, stirring to deglaze and scraping up any caramelized bits from the bottom.
05 -
Return the browned beef and any resting juices to the dish. Pour in beef broth and add thyme sprigs. Stir together and bring to a gentle boil.
06 -
Cover the casserole with its lid and transfer to the oven. Cook for 90 minutes.
07 -
Remove from the oven, uncover, and stir in halved chestnut mushrooms. Re-cover and return to the oven for a further 90 minutes.
08 -
Once the stew is tender and rich, remove from oven. Carefully discard thyme sprigs. Season to taste with additional salt and pepper. Stir in half of the chopped parsley for freshness, and scatter the remainder over the surface as garnish. Serve hot, ideally with mashed potatoes or rustic bread.