Preheat the oven to 200C/400F and line a large baking tray with grease proof paper.
Place the chunks of apples, cornflour, cinnamon, nutmeg, salt, brown sugar and vanilla extract into a large bowl and stir to cover all the apples in the sugar mixture. Leave to one side.
Place one sheet of filo pastry onto your prepared baking tray, then lightly brush with melted butter. Place the next sheet of pastry onto the melted butter brushed pastry sheet. Repeat the brushing of butter and placing of the next pastry sheet, until you've used all of your sheets of pastry. Don't brush the final sheet of pastry with butter.
Tip the apple filling into a line along the centre of the pastry, long ways, leaving a 1 inch gap at either end and 2-3 inches each side of the filling.
Brush along each of the edges of pastry with melted butter. Take one long edge of the pastry and lift over the apple filling. Then take the other long side of pastry and bring up over the apple filling, this one should also go over the pastry you already folded over the apples to create a seam.
Gently press to make sure the seam is stuck and then take the filo roll in both of your hands and flip over so the seam is on the bottom of the tray.
Trim either end of the pastry, so there's only a tiny bit of overhang after the apple filing ends.
Brush the top of the filo roll with the remaining melted butter and place in the oven for 15 minutes at 200C/400F. After 15 minutes, turn the oven down to 180C/350F and cook for a further 15-20 minutes.
Once golden and flaky, remove from the oven and test the middle - I took a skewer and gently stuck it into the middle of the strudel to feel the resistance of the apples. They should be soft and tender.
Leave to cool for at least 30 minutes before serving. Cut into 8-10 slices and serve with ice cream, powdered sugar or caramel sauce!
Easy Apple Strudel will keep in an airtight container, at room temperature, for 3 days.