1.Cut the beef into 3cm pieces. Heat the oil in a large casserole dish or heavy-based saucepan over medium-high heat. Cook beef, in batches, until browned, transferring to a plate as it is cooked.
2.Add the onion and garlic to the pan; cook, stirring for a few minutes or until softened.
3.Add the beef, tomato paste, tomatoes, stock and bay leaf. Bring to the boil, then reduce to a simmer; cook, covered, for 30 minutes.
4.Add the mushrooms and continue to simmer for a further hour, stirring occasionally. Season to taste with salt and freshly ground black pepper.
5.Boil the potatoes until cooked through. Drain and allow the potatoes to dry off.
6.In a saucepan, heat the milk until just before boiling, add the potatoes and butter, and gently mash together. Add the parmesan and stir to combine. Season to taste with sea salt and ground white pepper.
7.Serve the Beef Stew with the Parmesan Mash and a sprinkle of chopped parsley.