Preheat the oven to 160ºC. Spray a casserole pan with low-calorie cooking spray and set on a medium heat. Then add the beef and fry for 5 minutes, until browned on all sides. Add the onion and mushrooms, and fry for a further 5 minutes.
Add the stock cube to the water and stir until dissolved. Then pour into the pan — along with the red wine vinegar, Henderson’s relish, tomato puree, and stock pot.
Add the cornflour to the cold water and mix until smooth. Pour into the beef mixture and stir well.
Cover with a lid and cook in the oven for 1 hour 30 minutes.
Pour the pie filling into an ovenproof dish. Increase the oven temperature to 180ºC, and leave the filling to cool slightly while the oven preheats.
Scrunch the filo pastry sheets and lay on-top of the pie filling. Spray with low-calorie cooking spray.
Place in the oven, and cook for 15-20 minutes — until golden brown and crisp. Serve with your choice of accompaniment.