Spray the Instant Pot/pressure cooker with low calorie cooking sprray and place into Sauté mode. Brown the steak in batches until it has browned then set aside.
Deglaze the pan with some of the beef stock, making sure there is nothing stuck to the bottom of the pan. Add the onions, mushrooms, red wine vinegar, Worcestershire sauce, tomato puree, stock pot (optional), and beef stock to the pan and stir well.
When the liquid starts to bubble add the steak and lock the lid. Place on Manual for 30 minutes. Make sure the valve on top is set to sealing and allow the Instant Pot/pressure cooker to release manually for 20 minutes after cooking.
Remove the lid and place the Instant Pot/pressure cooker back into Sauté mode and reduce the mixture until it reaches your desired thickness - you can also add some cornflour to thicken up if you don't wish to wait, but remember to adjust the calories/Points.
Spray a frying pan with low calorie cooking spray and brown the steak in batches. Place into the slow cooker.
Remove the lid and cook for a further hour & reduce the mixture until it reaches your desired thickness - you can also add some cornflour to thicken up if you don't wish to wait, but remember to adjust the calories/Points.
Pour the pie filling into an oven proof dish (we used a 19 cm shallow dish but you can use a smaller deeper one if you want).
Take one sheet of filo, lay it out flat and spray generously with low calorie cooking spray.
Cut the sheet into 8 even pieces. Scrunch each piece up lightly then place them on top of the pie filling. Try to leave as fewer gaps as possible.
Spray with a little more low calorie cooking spray.
Place the dish on a baking tray (just in case it drips) and cook for 15-20 minutes at 180°C or until the filo is golden brown and crisp all over.
Remove from the oven and serve.