Pre-heat oven to 180°C (160°C fan-forced).
Heat half the oil in a large heavy based pan. Add beef and sear in batches until browned all over. Set aside.
Add remaining oil to pan and cook the onion, carrot, celery and garlic until tender. Sprinkle flour over vegetables and mix well, cooking for 1 minute. Pour stock in slowly, mixing to bring together.
Return seared beef to the pot with the water, tomato paste and worcestershire sauce. Bring to the boil, reduce heat and simmer covered for 1 ½ hours until beef is tender. Stir in parsley and season to taste.
Meanwhile; place potatoes into a large saucepan of water and bring to the boil. Cook for 15 minutes until tender. Drain well and mash with half of the butter. Stir in milk until smooth.
Spoon beef into a 10 cup capacity baking dish. Spread potato mixture evenly over beef and scatter with the remaining butter. Bake for 45 minutes until golden and crisp around the edges.