Put the flour and salt in a food processor, whizz and drizzle in the oil and water. Process the dough about a minute until it forms a ball. Remove to a floured surface and knead until smooth, about 3 minutes. Place in a bowl, cover with a cloth and refrigerate 2 hours.
Preheat oven to 200 degrees C and lightly oil a pizza tray.
Making the filling:
Finely chop the silverbeet leaves and stalks. Place in a colander and toss with the tablespoon salt. Leave for 20 minutes then rinse and squeeze dry in a cloth.
Transfer silverbeet to a bowl with the chopped potato, diced onion, parsley and cheese. Season with pepper. Whisk the egg with 1 tablespoon extra virgin olive oil and mix through. Taste for salt.
roll 2/3 of the dough on a floured surface into a circle that will cover the base of the pizza tray.
Spoon on the filling, leaving a 2cm border of dough.
Stretch back the edge of the dough over the filling, pleating as you go. Dampen with water. Roll remaining dough a little smaller and drape over the filling. Press to seal with the pleated edge. Pierce here and there with a fork then drizzle the top with remaining tablespoon olive oil. Scatter over a few grains of sea salt.
Bake 20 minutes or until golden. Let cool 10 minutes before cutting.