Place the casserole steak in a bowl, add the plain flour and combine well until the meat is coated in the flour.
Heat the olive oil in a saucepan and over a medium heat and sauté the onion until soft. Then add the coated meat and cook for 10 minutes until browned. Stirring frequently to prevent the meat sticking to the pan.
Transfer the contents of the pan to a casserole dish, add the Worcestershire sauce and beef stock, stir well and then season with the salt and pepper.
Cook in oven for 50m - 1 hour until the meat is tender.
Transfer the contents of the casserole to a pie dish.
Take each individual sheet of filo pastry and crumple it into a loose ball. Then place the 4 sheets on top of the pie dish. Spray the filo balls with the cooking oil.
Place the pie dish back into the oven and bake for about 15 - 20 minutes until the filo balls are lightly browned and crisp.