Preheat the oven to 180 °C (360 °F).
Mix the flour, water, vinegar and salt in a bowl. Knead until you achieve a smooth dough.
Wrap the dough in plastic wrap and set aside for 30 minutes to rest.
Once the dough has rested, cut it in half and sprinkle your worktop with corn flour. Take one piece of dough and begin to roll it out slightly with your hands.
Using a rolling pin, roll the dough out till it is a few millimeters thick and 32cm (12 inches) wide. Turn the dough slightly each time you roll it out. Roll it out by first rolling the dough up on the rolling pin, then rolling it out. Repeat with the other piece of dough.
Place one sheet of dough in a 30cm (12 inch) round baking pan, greased with olive oil. Spread the filling mixture evenly over the top and cover with the second sheet of dough.
Press the edges together well, brush with olive oil and bake for 1 hour, until the pie is golden.
Remove from the oven and let it cool slightly before slicing and serving.