First things first, pop the flour and salt into large bowl and mix together. Slowly pour in the water and oil mixing together as you add it. You can use a freestanding mixer with a dough hook attachment or a fork and mix by hand. 

Once combined beat your dough together for about 5 minutes until you have a smooth dough which is still slightly sticky.

Pop your dough onto your work surface dusted with cornflour. Divide your dough into 12 equal pieces and roll each piece into a ball. Pop onto a baking tray dusted with corn flour making sure your balls of dough are spaced slightly apart, you might need to put spread your dough across 2 trays to ensure there is enough space between each piece. 

Dust the balls of filo dough with corn flour and cover with a damp tea towel. Leave your dough to rest for 2 hours.

Once your dough has rested, roll each piece of dough on a surface dusted with corn flour. Make sure you use plenty of cornflour on your dough and rolling pin as the dough will be a bit sticky. Roll your dough into a rectangle about ¼ cm thickness. 

Once you have rolled out a sheet of filo, place on a piece of baking parchment dusted with corn flour. Then dust the sheet of filo with cornflour and cover with a damp tea towel. Place the next sheet of filo on top of the previous sheet and then cover with the damp tea towel, repeat until you have rolled out all 12 sheets of filo.

You filo pastry is now ready to use or keep refrigerated and covered with cling film to prevent it drying out.