1. Heat the oil in a large non-stick pan on a medium heat on the hob. Working in two batches, add the meat and fry for a few minutes until cooked on all sides. Drain off and keep any cooking liquid that comes off the beef to one side.
2. Next add the onions and cook on a medium-high heat for 4 minutes until translucent, before adding the mushrooms, Cook for a further 4 minutes.
3. In a small bowl, add the Dijon mustard, Worcestershire sauce and flour. Add a few tablespoons of the beef stock and mix with a spoon until it’s a smooth paste.
4. Add the rest of the beef stock to the pan and bring up to the boil. Reduce the heat and then slowly add the mustard paste to the casserole, stirring well to make sure there’s no lumps. Bring back up to a high heat to allow the liquid to thicken.
5. Add the thyme, and season to taste with salt and pepper before transferring to an ovenproof dish.
6. Place in a preheated oven (190c / 170c fan) for 2 to 2.5 hours, until the meat is tender.
7. Whilst the casserole is in the oven, boil the carrots until just cooked. Drain and cool and set aside until the casserole is ready.
8. Add the carrots to the casserole just before serving, and garnish with a sprinkling of freshly-chopped parsley.