Preheat the oven to 170°C/Gas 3.
Toss the diced beef in the flour and season well with salt and pepper.
Heat the oil in a heavy-based, deep casserole dish (with a lid) and brown the beef, in batches if necessary.
Return all the meat to the pan and then add the sliced onions, carrots, beetroot and the thyme leaves. Generously season with salt and pepper and mix well.
Arrange the sliced potatoes on top of the meat and vegetable mix. Take care to make the potato layer nice and neat. Pour over just enough stock to come up to the bottom of the potato layer.
Cover with the lid and bake in the oven for about 1½ hours.
Remove the lid and return to the oven for a further 30 minutes to crisp the potatoes.